diff --git a/src/handler.ts b/src/handler.ts
index a893b28..f8cb262 100644
--- a/src/handler.ts
+++ b/src/handler.ts
@@ -1,5 +1,7 @@
+import type { APIGatewayProxyEventV2 } from 'aws-lambda';
 import { createSlackApp } from './app.ts';
 import { loadEnv } from './env.ts';
+import { isSlackRetryDueToTimeout } from './lib/slackRetry.ts';
 
 const env = loadEnv();
 const { receiver } = createSlackApp(env);
@@ -9,11 +11,16 @@ const { receiver } = createSlackApp(env);
 // AwsLambdaReceiverのハンドラーを2引数のasync関数でラップする
 // ref: https://github.com/slackapi/bolt-js/issues/2761
 export const handler = async (
-	event: Record<string, unknown>,
+	event: APIGatewayProxyEventV2,
 	context: unknown,
 ) => {
+	if (isSlackRetryDueToTimeout(event.headers)) {
+		console.log('skipped: slack retry (http_timeout)', {
+			retryNum: event.headers['x-slack-retry-num'],
+		});
+		return { statusCode: 200, body: 'ok (retry skipped)' };
+	}
+
 	const boltHandler = await receiver.start();
-	// boltHandlerは内部的にcallbackを使用しないが、型定義上3引数が必須
-	// biome-ignore lint/suspicious/noExplicitAny: AwsEventの型がexportされていないため
-	return boltHandler(event as any, context, () => {});
+	return boltHandler(event, context, () => {});
 };
diff --git a/src/lib/__tests__/slackRetry.test.ts b/src/lib/__tests__/slackRetry.test.ts
new file mode 100644
index 0000000..abe3b3e
--- /dev/null
+++ b/src/lib/__tests__/slackRetry.test.ts
@@ -0,0 +1,28 @@
+import assert from 'node:assert/strict';
+import { describe, it } from 'node:test';
+import { isSlackRetryDueToTimeout } from '../slackRetry.ts';
+
+describe('isSlackRetryDueToTimeout', () => {
+	it('http_timeoutのリトライの場合はtrueを返す', () => {
+		const headers = {
+			'x-slack-retry-num': '1',
+			'x-slack-retry-reason': 'http_timeout',
+		};
+		assert.equal(isSlackRetryDueToTimeout(headers), true);
+	});
+
+	it('http_timeout以外のリトライの場合はfalseを返す', () => {
+		const headers = {
+			'x-slack-retry-num': '1',
+			'x-slack-retry-reason': 'http_error',
+		};
+		assert.equal(isSlackRetryDueToTimeout(headers), false);
+	});
+
+	it('x-slack-retry-numヘッダーがない場合はfalseを返す', () => {
+		const headers = {
+			'content-type': 'application/json',
+		};
+		assert.equal(isSlackRetryDueToTimeout(headers), false);
+	});
+});
diff --git a/src/lib/slackRetry.ts b/src/lib/slackRetry.ts
new file mode 100644
index 0000000..d2a6308
--- /dev/null
+++ b/src/lib/slackRetry.ts
@@ -0,0 +1,10 @@
+import type { APIGatewayProxyEventV2 } from 'aws-lambda';
+
+export function isSlackRetryDueToTimeout(
+	headers: APIGatewayProxyEventV2['headers'],
+): boolean {
+	return (
+		!!headers['x-slack-retry-num'] &&
+		headers['x-slack-retry-reason'] === 'http_timeout'
+	);
+}