diff --git a/.github/workflows/check_review_status.yml b/.github/workflows/check_review_status.yml
deleted file mode 100644
index 56d791f26..000000000
--- a/.github/workflows/check_review_status.yml
+++ /dev/null
@@ -1,35 +0,0 @@
-name: 'Check review status'
-
-on:
-  pull_request_review:
-    types: [submitted, edited, dismissed]
-
-jobs:
-  check_review_status:
-    runs-on: 'ubuntu-latest'
-    permissions:
-      pull-requests: read
-      contents: read
-    env:
-      BASE_SHA: ${{ github.event.pull_request.base.sha }}
-      HEAD_SHA: ${{ github.event.pull_request.head.sha }}
-      PR_AUTHOR: ${{ github.event.pull_request.user.login }}
-      GH_REPO: ${{ github.repository }}
-    steps:
-      - uses: actions/checkout@v4
-        with:
-          filter: 'blob:none'
-          fetch-depth: 0
-          ref: main
-      - name: Changed gems and non gem files
-        id: changes
-        run: |
-          ruby .github/workflows/pr_bot/changed_files.rb
-      - name: Check review status
-        env:
-          CHANGED_GEMS: ${{ steps.changes.outputs.gems }}
-          CHANGED_NON_GEMS: ${{ steps.changes.outputs.non_gems }}
-          PR_NUMBER: ${{ github.event.pull_request.number }}
-          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-        run: |
-          ruby .github/workflows/pr_bot/check_review_status.rb "$CHANGED_GEMS" "$CHANGED_NON_GEMS" "$PR_NUMBER"
diff --git a/.github/workflows/comment_on_review.yml b/.github/workflows/comment_on_review.yml
new file mode 100644
index 000000000..6eec4b143
--- /dev/null
+++ b/.github/workflows/comment_on_review.yml
@@ -0,0 +1,29 @@
+name: Comment on review
+
+on:
+  workflow_run:
+    workflows: [Generate comment body on review]
+    types: [completed]
+
+
+jobs:
+  comment:
+    runs-on: ubuntu-latest
+    if: ${{ github.event.workflow_run.conclusion == 'success' }}
+    permissions:
+      pull-requests: write
+      actions: read
+    steps:
+      - name: Download artifact
+        uses: actions/download-artifact@v4
+        with:
+          name: comment_body_on_review
+          run-id: ${{ github.event.workflow_run.id}}
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+      - name: Send a comment
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GH_REPO: ${{ github.repository }}
+        run:
+          gh pr comment "$(cat PR_NUMBER)" --body "$(cat COMMENT_BODY.txt)" --repo "$GH_REPO"
+
diff --git a/.github/workflows/generate_comment_body_on_review.yml b/.github/workflows/generate_comment_body_on_review.yml
new file mode 100644
index 000000000..58324a1c3
--- /dev/null
+++ b/.github/workflows/generate_comment_body_on_review.yml
@@ -0,0 +1,56 @@
+# This workflow generates a comment body on an approval.
+# It generates the body and saves it as an artifact.
+# A following workflow called from `workflow_run` event uses the artifact.
+#
+# These workflows are separated due to GITHUB_TOKEN's permission.
+# GitHub does not allow `write` permission on public fork repositories on `pull_request_review` event.
+# Therefore we need to use `workflow_run` event to permit `write` actions to the token.
+
+name: 'Generate comment body on review'
+
+on:
+  pull_request_review:
+    types: [submitted]
+
+jobs:
+  create_comment:
+    if: github.event.review.state != 'CHANGES_REQUESTED'
+    runs-on: 'ubuntu-latest'
+    env:
+      BASE_SHA: ${{ github.event.pull_request.base.sha }}
+      HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+      PR_AUTHOR: ${{ github.event.pull_request.user.login }}
+      GH_REPO: ${{ github.repository }}
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          filter: 'blob:none'
+          fetch-depth: 0
+          ref: main
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: '3.3'
+          bundler-cache: true
+      - name: Changed gems and non gem files
+        id: changes
+        run: |
+          ruby .github/workflows/pr_bot/changed_files.rb
+      - name: Prepare comment body
+        id: comment-body
+        env:
+          CHANGED_GEMS: ${{ steps.changes.outputs.gems }}
+          CHANGED_NON_GEMS: ${{ steps.changes.outputs.non_gems }}
+          PR_NUMBER: ${{ github.event.pull_request.number }}
+          REVIEWED_BY: ${{ github.event.review.user.login }}
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          ruby .github/workflows/pr_bot/review_result_comment_body.rb "$CHANGED_GEMS" "$CHANGED_NON_GEMS" "$PR_NUMBER" COMMENT_BODY.txt
+          echo "$PR_NUMBER" > PR_NUMBER
+      - name: Store comment body
+        uses: actions/upload-artifact@v4
+        with:
+          name: comment_body_on_review
+          path: |
+            COMMENT_BODY.txt
+            PR_NUMBER
+          retention-days: 1
diff --git a/.github/workflows/merge_on_comment.yml b/.github/workflows/merge_on_comment.yml
index ad48bfe9d..8bd2703d4 100644
--- a/.github/workflows/merge_on_comment.yml
+++ b/.github/workflows/merge_on_comment.yml
@@ -5,8 +5,24 @@ on:
     types: [created]
 
 jobs:
+  is_merge_command:
+    if: ${{ github.event.issue.pull_request }}
+    runs-on: 'ubuntu-latest'
+    outputs:
+      is_merge_command: ${{ steps.set_is_merge_command.outputs.is_merge_command }}
+    steps:
+      - name: Set is_merge_command
+        id: set_is_merge_command
+        env:
+          COMMENT_BODY: ${{ github.event.comment.body }}
+        run: |
+          ruby -e '
+            is_merge_command = ENV["COMMENT_BODY"].match?(%r!\A/merge\s*\z!)
+            puts "is_merge_command=#{is_merge_command}"
+          ' >> $GITHUB_OUTPUT
   merge:
-    if: ${{ github.event.issue.pull_request && github.event.comment.body == '/merge' }}
+    needs: is_merge_command
+    if: ${{ needs.is_merge_command.outputs.is_merge_command == 'true' }}
     runs-on: 'ubuntu-latest'
     permissions:
       pull-requests: write
@@ -17,6 +33,10 @@ jobs:
           filter: 'blob:none'
           fetch-depth: 0
           ref: main
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: '3.3'
+          bundler-cache: true
       - name: Fetch PR information
         id: pr_info
         env:
@@ -45,11 +65,12 @@ jobs:
           HEAD_SHA: ${{ steps.pr_info.outputs.head_sha }}
           PR_AUTHOR: ${{ steps.pr_info.outputs.author }}
           CHANGED_GEMS: ${{ steps.changes.outputs.gems }}
+          CHANGED_NON_GEMS: ${{ steps.changes.outputs.non_gems }}
 
-          COMMENTED_BY: ${{ github.event.issue.user.login }}
+          COMMENTED_BY: ${{ github.event.comment.user.login }}
           PR_NUMBER: ${{ github.event.issue.number }}
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           GH_REPO: ${{ github.repository }}
         run: |
-          ruby .github/workflows/pr_bot/check_merge_ability.rb "$CHANGED_GEMS"
-          gh pr merge "$PR_NUMBER" --repo "$GH_REPO" --merge
+          ruby .github/workflows/pr_bot/check_merge_ability.rb "$CHANGED_GEMS" "$CHANGED_NON_GEMS" "$PR_NUMBER"
+          gh pr merge "$PR_NUMBER" --repo "$GH_REPO" --squash
diff --git a/.github/workflows/pr_bot/changed_files.rb b/.github/workflows/pr_bot/changed_files.rb
index 6ce1a7809..ccf9cca6e 100644
--- a/.github/workflows/pr_bot/changed_files.rb
+++ b/.github/workflows/pr_bot/changed_files.rb
@@ -1,6 +1,6 @@
 require_relative "./utils"
 
-paths = `git diff --name-only -z #{BASE_SHA} #{HEAD_SHA}`.split("\0")
+paths = `git diff --name-only -z #{BASE_SHA}...#{HEAD_SHA}`.split("\0")
 changed_gems = paths.select { _1.start_with?("gems/") }.map { _1.split("/")[1] }.uniq
 changed_non_gems = paths.reject { _1.start_with?("gems/") }
 
diff --git a/.github/workflows/pr_bot/check_merge_ability.rb b/.github/workflows/pr_bot/check_merge_ability.rb
index dd43037fd..36e70ec67 100644
--- a/.github/workflows/pr_bot/check_merge_ability.rb
+++ b/.github/workflows/pr_bot/check_merge_ability.rb
@@ -1,17 +1,34 @@
 require_relative "./utils"
+require_relative "./merge_ability"
 
-def can_merge?(commented_by, author, gem_reviewers)
-  return true if commented_by == author
-  return true if administorators.include?(commented_by)
-  return true if gem_reviewers.include?(commented_by)
-  return false
+def comment_to_github(body, pr_number)
+  sh! 'gh', 'pr', 'comment', pr_number, '--body', body, '--repo', GH_REPO
 end
 
-def all_gem_reviewers(changed_gems)
-  changed_gems.flat_map { |gem| gem_reviewers(gem, BASE_SHA) }
+changed_gems = JSON.parse(ARGV[0])
+changed_non_gems = JSON.parse(ARGV[1])
+pr_number = ARGV[2]
+
+ability = MergeAbility.new(changed_gems:, changed_non_gems:, pr_number:)
+
+unless ability.can_merge_by?(ENV['COMMENTED_BY'], PR_AUTHOR)
+  body = <<~BODY
+    `/merge` command failed.
+
+    You do not have permission to merge this PR.
+    PR author, reviewers, and administrators can merge this PR.
+  BODY
+  comment_to_github(body, pr_number)
+  exit 1
 end
 
-reviewers = all_gem_reviewers(JSON.parse(ARGV[0]))
-return if can_merge?(ENV['COMMENTED_BY'], PR_AUTHOR, reviewers)
+unless ability.approved?
+  body  = <<~BODY
+    `/merge` command failed.
 
-raise "You do not have permission to merge this PR."
+    This PR is not approved yet by the reviewers. Please get approval from the reviewers.
+    See the Actions tab for detail.
+  BODY
+  comment_to_github(body, pr_number)
+  exit 1
+end
diff --git a/.github/workflows/pr_bot/check_review_status.rb b/.github/workflows/pr_bot/check_review_status.rb
deleted file mode 100644
index 8785d2695..000000000
--- a/.github/workflows/pr_bot/check_review_status.rb
+++ /dev/null
@@ -1,49 +0,0 @@
-require_relative "./utils"
-require "json"
-
-def gem_accepted?(gem, approvers)
-  reviewers = gem_reviewers(gem, BASE_SHA)
-
-  # If reviewers is empty, it means that anyone cannot approve this PR.
-  # So, we can merge this PR without approval.
-  return true if reviewers.empty?
-
-  # If the author is a reviewer, they can merge this PR themselves.
-  return true if reviewers.include?(PR_AUTHOR)
-
-  not (reviewers & approvers).empty?
-end
-
-def non_gem_accepted?(approvers)
-  admins = administorators.map { _1['login'] }
-
-  not (approvers & admins).empty?
-end
-
-def main(changed_gems, changed_non_gems, pr_number)
-  approvers = approvements(HEAD_SHA, pr_number).map { _1['user']['login'] }
-
-  status = 0
-
-  # Check gem files
-  not_approved_gems = changed_gems.reject { |gem| gem_accepted?(gem, approvers) }
-  unless not_approved_gems.empty?
-    puts "The following gems are not approved yet:"
-    puts not_approved_gems.join("\n")
-    status = 1
-  end
-
-  # Check non gem files
-  if !changed_non_gems.empty? && !non_gem_accepted?(approvers)
-    puts "The following files are changed, but not approved by the admin yet:"
-    puts changed_non_gems.join("\n")
-    status = 1
-  end
-
-  exit status
-end
-
-changed_gems = JSON.parse(ARGV[0])
-changed_non_gems = JSON.parse(ARGV[1])
-pr_number = ARGV[2]
-main(changed_gems, changed_non_gems, pr_number)
diff --git a/.github/workflows/pr_bot/merge_ability.rb b/.github/workflows/pr_bot/merge_ability.rb
new file mode 100644
index 000000000..86c8b2a53
--- /dev/null
+++ b/.github/workflows/pr_bot/merge_ability.rb
@@ -0,0 +1,72 @@
+require_relative "./utils"
+
+class MergeAbility
+  attr_reader :changed_gems, :changed_non_gems, :pr_number
+
+  def initialize(changed_gems:, changed_non_gems:, pr_number:)
+    @changed_gems = changed_gems
+    @changed_non_gems = changed_non_gems
+    @pr_number = pr_number
+  end
+
+  def approved?
+    is_approved = true
+
+    # Check gem files
+    unless not_approved_gems.empty?
+      log "The following gems are not approved yet:"
+      log not_approved_gems.join("\n")
+      is_approved = false
+    end
+
+    # Check non gem files
+    if waiting_admin_approval?
+      log "The following files are changed, but not approved by the admin yet:"
+      log changed_non_gems.join("\n")
+      is_approved = false
+    end
+
+    is_approved
+  end
+
+  def can_merge_by?(commented_by, author)
+    return true if commented_by == author
+    return true if administorators.include?(commented_by)
+    return true if all_gem_reviewers.include?(commented_by)
+    return false
+  end
+
+  def not_approved_gems
+    @not_approved_gems ||= changed_gems.reject { |gem| gem_accepted?(gem) }
+  end
+
+  def waiting_admin_approval?
+    return false if changed_non_gems.empty?
+
+    admins = administorators.map { _1['login'] }
+    (approvers & admins).empty?
+  end
+
+  private
+
+  def all_gem_reviewers
+    @all_gem_reviewers ||= changed_gems.flat_map { |gem| gem_reviewers(gem, BASE_SHA) }
+  end
+
+  def gem_accepted?(gem)
+    reviewers = gem_reviewers(gem, BASE_SHA)
+
+    # If reviewers is empty, it means that anyone cannot approve this PR.
+    # So, we can merge this PR without approval.
+    return true if reviewers.empty?
+
+    # If the author is a reviewer, they can merge this PR themselves.
+    return true if reviewers.include?(PR_AUTHOR)
+
+    not (reviewers & approvers).empty?
+  end
+
+  def approvers
+    @approvers ||= approvements(HEAD_SHA, pr_number).map { _1['user']['login'] }
+  end
+end
diff --git a/.github/workflows/pr_bot/review_result_comment_body.rb b/.github/workflows/pr_bot/review_result_comment_body.rb
new file mode 100644
index 000000000..1002b3253
--- /dev/null
+++ b/.github/workflows/pr_bot/review_result_comment_body.rb
@@ -0,0 +1,35 @@
+require_relative "./merge_ability"
+
+changed_gems = JSON.parse(ARGV[0])
+changed_non_gems = JSON.parse(ARGV[1])
+pr_number = ARGV[2]
+file = ARGV[3]
+
+ability = MergeAbility.new(changed_gems:, changed_non_gems:, pr_number:)
+
+reviewer = ENV['REVIEWED_BY']
+
+msg = "Thanks for your review, @#{reviewer}!\n\n"
+
+if ability.approved?
+  msg << <<~MSG
+    @#{PR_AUTHOR}, @#{reviewer} This PR is ready to be merged.
+    Just comment `/merge` to merge this PR.
+  MSG
+else
+  unless ability.not_approved_gems.empty?
+    msg << <<~MSG
+      This PR still needs approval from the reviewers of the following gems.
+      #{ability.not_approved_gems.map { "* `#{_1}`" }.join("\n")}
+    MSG
+  end
+  if ability.waiting_admin_approval?
+    msg << <<~MSG
+      This PR still needs approval from the administrators.
+    MSG
+  end
+
+  msg << "Please get approval from the reviewers."
+end
+
+File.write(file, msg)
diff --git a/.github/workflows/pr_bot/utils.rb b/.github/workflows/pr_bot/utils.rb
index fb273ae27..071c1be95 100644
--- a/.github/workflows/pr_bot/utils.rb
+++ b/.github/workflows/pr_bot/utils.rb
@@ -63,7 +63,12 @@ def gh_api!(*args)
 
 def approvements(sha, pr_number)
   reviews = gh_api! "/repos/#{GH_REPO}/pulls/#{pr_number}/reviews"
-  reviews.select { _1['state'] == 'APPROVED' && _1['commit_id'] == sha }
+  reviews.select do
+    _1['commit_id'] == sha && (
+      _1['state'] == 'APPROVED' ||
+        (_1['body'].include?('APPROVE') && _1['state'] == 'COMMENTED')
+    )
+  end
 end
 
 def administorators
diff --git a/.github/workflows/pr_bot/welcome_comment_body.rb b/.github/workflows/pr_bot/welcome_comment_body.rb
index 9424d8afe..cd9d7ddd2 100644
--- a/.github/workflows/pr_bot/welcome_comment_body.rb
+++ b/.github/workflows/pr_bot/welcome_comment_body.rb
@@ -55,7 +55,8 @@
       msg << <<~MSG
         You need to get approval from the reviewers of this gem.
 
-        #{reviewers.map { "@#{_1}" }.join(', ')}, please review and approve the changes.
+        #{reviewers.map { "@#{_1}" }.join(', ')}, please review this pull request.
+        If this change is acceptable, please make a review comment including `APPROVE`.
         After that, the PR author or the reviewers can merge this PR.
         Just comment `/merge` to merge this PR.
       MSG
@@ -76,7 +77,8 @@
       msg << <<~MSG
         You need to get approval from the reviewers of this gem.
 
-        #{reviewers.map { "@#{_1}" }.join(', ')}, please review and approve the changes.
+        #{reviewers.map { "@#{_1}" }.join(', ')}, please review this pull request.
+        If this change is acceptable, please make a review comment including `APPROVE`.
         After that, the PR author or the reviewers can merge this PR.
         Just comment `/merge` to merge this PR.
       MSG
diff --git a/.github/workflows/welcome_comment.yml b/.github/workflows/welcome_comment.yml
index 242842e13..9251ba2a2 100644
--- a/.github/workflows/welcome_comment.yml
+++ b/.github/workflows/welcome_comment.yml
@@ -1,7 +1,7 @@
 name: 'Test PR comment'
 
 on:
-  pull_request:
+  pull_request_target:
     types: [opened]
 
 jobs:
@@ -21,10 +21,13 @@ jobs:
           filter: 'blob:none'
           fetch-depth: 0
           ref: main
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: '3.3'
+          bundler-cache: true
       - name: Changed gems and non gem files
         id: changes
         run: |
-          # TODO: checkout the main branch
           ruby .github/workflows/pr_bot/changed_files.rb
       - name: Prepare comment body
         id: comment-body
@@ -33,11 +36,10 @@ jobs:
           CHANGED_NON_GEMS: ${{ steps.changes.outputs.non_gems }}
         run: |
           ruby .github/workflows/pr_bot/welcome_comment_body.rb "$CHANGED_GEMS" "$CHANGED_NON_GEMS"
-      - name: test message
+      - name: Send a comment
         env:
           PR_NUMBER: ${{ github.event.pull_request.number }}
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-          GH_REPO: ${{ github.repository }}
           COMMENT_BODY: ${{ steps.comment-body.outputs.welcome_comment_body }}
         run:
           gh pr comment "$PR_NUMBER" --body "$COMMENT_BODY" --repo "$GH_REPO"