diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 61280dd..79f81c3 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -11,6 +11,14 @@ jobs:
       BUNDLE_GEMFILE: ${{ github.workspace }}/test/using_bundler/Gemfile
     steps:
       - uses: actions/checkout@v4
+      - name: Fetch all commits for PR branch plus head commit of base branch
+        run: |
+          # fetch all commits of the PR branch
+          git fetch --shallow-exclude "${{ github.base_ref }}" origin "${{ github.ref }}"
+          # fix for "fatal: error in object: unshallow"
+          git repack -d
+          # fetch head commit of base branch
+          git fetch --deepen 1 origin "${{ github.ref }}"
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: 2.6
diff --git a/README.md b/README.md
index 1ae8817..07caf3d 100644
--- a/README.md
+++ b/README.md
@@ -98,6 +98,11 @@ Optional. Do not install Rubocop or its extensions. Default: `false`.
 
 Optional. Run Rubocop with bundle exec. Default: `false`.
 
+### `only_changed`
+
+Optional. Run Rubocop only on changed (and added) files, for speedup [`true`, `false`].
+Default: `false`.
+
 ## Example usage
 
 This action will use your [RuboCop Configuration](https://docs.rubocop.org/rubocop/configuration.html) automatically.
diff --git a/action.yml b/action.yml
index 7cd76cc..d7e8b2f 100644
--- a/action.yml
+++ b/action.yml
@@ -46,6 +46,9 @@ inputs:
   use_bundler:
     description: "Run Rubocop with bundle exec. Default: `false`"
     default: 'false'
+  only_changed:
+    description: "Run Rubocop only on changed (and added) files, for speedup [`true`, `false`]"
+    default: 'false'
 runs:
   using: 'composite'
   steps:
@@ -68,6 +71,9 @@ runs:
         INPUT_WORKDIR: ${{ inputs.workdir }}
         INPUT_SKIP_INSTALL: ${{ inputs.skip_install }}
         INPUT_USE_BUNDLER: ${{ inputs.use_bundler }}
+        INPUT_ONLY_CHANGED: ${{ inputs.only_changed }}
+        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..f247c82 100755
--- a/script.sh
+++ b/script.sh
@@ -1,4 +1,6 @@
-#!/bin/sh -e
+#!/usr/bin/env bash
+
+set -e
 
 cd "${GITHUB_WORKSPACE}/${INPUT_WORKDIR}" || exit
 export REVIEWDOG_GITHUB_API_TOKEN="${INPUT_GITHUB_TOKEN}"
@@ -85,9 +87,24 @@ else
   BUNDLE_EXEC="bundle exec "
 fi
 
+if [ "${INPUT_ONLY_CHANGED}" = "true" ]; then
+  echo '::group:: Getting changed files list'
+  readarray -t CHANGED_FILES < <(
+    comm -12 \
+      <(git diff --diff-filter=d --name-only "${BASE_REF}..${HEAD_REF}" | sort) \
+      <(${BUNDLE_EXEC}rubocop --list-target-files | sort)
+  )
+  echo "${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}" \