diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 61280dd..d235443 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -11,6 +11,8 @@ jobs:
       BUNDLE_GEMFILE: ${{ github.workspace }}/test/using_bundler/Gemfile
     steps:
       - uses: actions/checkout@v4
+        with:
+          fetch-depth: 2 # we are comparing PR merge head with base
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: 2.6
diff --git a/README.md b/README.md
index 551328c..7817571 100644
--- a/README.md
+++ b/README.md
@@ -47,6 +47,11 @@ Default is `added`.
 Optional. Report level for reviewdog [`info`, `warning`, `error`].
 It's same as `-level` flag of reviewdog.
 
+### `only_changed`
+
+Optional. Run Rubocop only on changed (and added) files, for speedup [`true`, `false`].
+Default: `false`.
+
 ### `reporter`
 
 Optional. Reporter of reviewdog command [`github-pr-check`, `github-check`, `github-pr-review`].
diff --git a/action.yml b/action.yml
index 8999993..3bd5ef3 100644
--- a/action.yml
+++ b/action.yml
@@ -19,6 +19,9 @@ inputs:
   level:
     description: 'Report level for reviewdog [info,warning,error]'
     default: 'error'
+  only_changed:
+    description: "Run Rubocop only on changed (and added) files, for speedup [`true`, `false`]"
+    default: 'false'
   reporter:
     description: |
       Reporter of reviewdog command [github-pr-check,github-check,github-pr-review].
@@ -61,6 +64,7 @@ runs:
         INPUT_FILTER_MODE: ${{ inputs.filter_mode }}
         INPUT_GITHUB_TOKEN: ${{ inputs.github_token }}
         INPUT_LEVEL: ${{ inputs.level }}
+        INPUT_ONLY_CHANGED: ${{ inputs.only_changed }}
         INPUT_REPORTER: ${{ inputs.reporter }}
         INPUT_REVIEWDOG_FLAGS: ${{ inputs.reviewdog_flags }}
         INPUT_RUBOCOP_EXTENSIONS: ${{ inputs.rubocop_extensions }}
@@ -70,6 +74,8 @@ runs:
         INPUT_TOOL_NAME: ${{ inputs.tool_name }}
         INPUT_USE_BUNDLER: ${{ inputs.use_bundler }}
         INPUT_WORKDIR: ${{ inputs.workdir }}
+        BASE_REF: ${{ github.event.pull_request.base.sha }}
+        HEAD_REF: ${{ github.sha }}
 branding:
   icon: 'check-circle'
   color: 'red'
diff --git a/script.sh b/script.sh
index 81a06bc..be46c4d 100755
--- a/script.sh
+++ b/script.sh
@@ -1,4 +1,7 @@
-#!/bin/sh -e
+#!/usr/bin/env bash
+
+set -e
+set -o pipefail
 
 cd "${GITHUB_WORKSPACE}/${INPUT_WORKDIR}" || exit
 export REVIEWDOG_GITHUB_API_TOKEN="${INPUT_GITHUB_TOKEN}"
@@ -85,9 +88,36 @@ else
   BUNDLE_EXEC="bundle exec "
 fi
 
+if [ "${INPUT_ONLY_CHANGED}" = "true" ]; then
+  echo '::group:: Getting changed files list'
+
+  # get intersection of changed files (excluding deleted) with target files for
+  # rubocop as an array
+  # shellcheck disable=SC2086
+  readarray -t CHANGED_FILES < <(
+    comm -12 \
+      <(git diff --diff-filter=d --name-only "${BASE_REF}..${HEAD_REF}" | sort || kill $$) \
+      <(${BUNDLE_EXEC}rubocop --list-target-files | sort || kill $$)
+  )
+
+  if (( ${#CHANGED_FILES[@]} == 0 )); then
+    echo "No relevant files for rubocop, skipping"
+    exit 0
+  fi
+
+  printf '%s\n' "${CHANGED_FILES[@]}"
+
+  if (( ${#CHANGED_FILES[@]} > 100 )); then
+    echo "More than 100 changed files (${#CHANGED_FILES[@]}), running rubocop on all files"
+    unset CHANGED_FILES
+  fi
+
+  echo '::endgroup::'
+fi
+
 echo '::group:: Running rubocop with reviewdog 🐶 ...'
 # shellcheck disable=SC2086
-${BUNDLE_EXEC}rubocop ${INPUT_RUBOCOP_FLAGS} --require ${GITHUB_ACTION_PATH}/rdjson_formatter/rdjson_formatter.rb --format RdjsonFormatter \
+${BUNDLE_EXEC}rubocop ${INPUT_RUBOCOP_FLAGS} --require ${GITHUB_ACTION_PATH}/rdjson_formatter/rdjson_formatter.rb --format RdjsonFormatter "${CHANGED_FILES[@]}" \
   | reviewdog -f=rdjson \
       -name="${INPUT_TOOL_NAME}" \
       -reporter="${INPUT_REPORTER}" \