diff --git a/src/api/endpoints/messaging/history.js b/src/api/endpoints/messaging/history.ts
similarity index 69%
rename from src/api/endpoints/messaging/history.js
rename to src/api/endpoints/messaging/history.ts
index 60c34a6a4..07ad6e0f2 100644
--- a/src/api/endpoints/messaging/history.js
+++ b/src/api/endpoints/messaging/history.ts
@@ -3,7 +3,7 @@
 /**
  * Module dependencies
  */
-import * as mongo from 'mongodb';
+import it from '../../it';
 import History from '../../models/messaging-history';
 import serialize from '../../serializers/messaging-message';
 
@@ -18,17 +18,8 @@ module.exports = (params, user) =>
 	new Promise(async (res, rej) =>
 {
 	// Get 'limit' parameter
-	let limit = params.limit;
-	if (limit !== undefined && limit !== null) {
-		limit = parseInt(limit, 10);
-
-		// From 1 to 100
-		if (!(1 <= limit && limit <= 100)) {
-			return rej('invalid limit range');
-		}
-	} else {
-		limit = 10;
-	}
+	const [limit, limitErr] = it(params.limit).expect.number().range(1, 100).default(10).qed();
+	if (limitErr) return rej('invalid limit param');
 
 	// Get history
 	const history = await History
diff --git a/src/api/endpoints/messaging/messages.js b/src/api/endpoints/messaging/messages.ts
similarity index 64%
rename from src/api/endpoints/messaging/messages.js
rename to src/api/endpoints/messaging/messages.ts
index eaaf38c39..81562efbc 100644
--- a/src/api/endpoints/messaging/messages.js
+++ b/src/api/endpoints/messaging/messages.ts
@@ -3,7 +3,7 @@
 /**
  * Module dependencies
  */
-import * as mongo from 'mongodb';
+import it from '../../it';
 import Message from '../../models/messaging-message';
 import User from '../../models/user';
 import serialize from '../../serializers/messaging-message';
@@ -21,47 +21,40 @@ module.exports = (params, user) =>
 	new Promise(async (res, rej) =>
 {
 	// Get 'user_id' parameter
-	let recipient = params.user_id;
-	if (recipient !== undefined && recipient !== null) {
-		recipient = await User.findOne({
-			_id: new mongo.ObjectID(recipient)
-		}, {
-			fields: {
-				_id: true
-			}
-		});
+	const [recipientId, recipientIdErr] = it(params.user_id).expect.id().required().qed();
+	if (recipientIdErr) return rej('invalid user_id param');
 
-		if (recipient === null) {
-			return rej('user not found');
+	// Fetch recipient
+	const recipient = await User.findOne({
+		_id: recipientId
+	}, {
+		fields: {
+			_id: true
 		}
-	} else {
-		return rej('user_id is required');
+	});
+
+	if (recipient === null) {
+		return rej('user not found');
 	}
 
 	// Get 'mark_as_read' parameter
-	let markAsRead = params.mark_as_read;
-	if (markAsRead == null) {
-		markAsRead = true;
-	}
+	const [markAsRead, markAsReadErr] = it(params.mark_as_read).expect.boolean().default(true).qed();
+	if (markAsReadErr) return rej('invalid mark_as_read param');
 
 	// Get 'limit' parameter
-	let limit = params.limit;
-	if (limit !== undefined && limit !== null) {
-		limit = parseInt(limit, 10);
+	const [limit, limitErr] = it(params.limit).expect.number().range(1, 100).default(10).qed();
+	if (limitErr) return rej('invalid limit param');
 
-		// From 1 to 100
-		if (!(1 <= limit && limit <= 100)) {
-			return rej('invalid limit range');
-		}
-	} else {
-		limit = 10;
-	}
+	// Get 'since_id' parameter
+	const [sinceId, sinceIdErr] = it(params.since_id).expect.id().qed();
+	if (sinceIdErr) return rej('invalid since_id param');
 
-	const since = params.since_id || null;
-	const max = params.max_id || null;
+	// Get 'max_id' parameter
+	const [maxId, maxIdErr] = it(params.max_id).expect.id().qed();
+	if (maxIdErr) return rej('invalid max_id param');
 
 	// Check if both of since_id and max_id is specified
-	if (since !== null && max !== null) {
+	if (sinceId !== null && maxId !== null) {
 		return rej('cannot set since_id and max_id');
 	}
 
@@ -73,20 +66,20 @@ module.exports = (params, user) =>
 			user_id: recipient._id,
 			recipient_id: user._id
 		}]
-	};
+	} as any;
 
 	const sort = {
 		_id: -1
 	};
 
-	if (since !== null) {
+	if (sinceId) {
 		sort._id = 1;
 		query._id = {
-			$gt: new mongo.ObjectID(since)
+			$gt: sinceId
 		};
-	} else if (max !== null) {
+	} else if (maxId) {
 		query._id = {
-			$lt: new mongo.ObjectID(max)
+			$lt: maxId
 		};
 	}
 
diff --git a/src/api/endpoints/messaging/messages/create.js b/src/api/endpoints/messaging/messages/create.ts
similarity index 72%
rename from src/api/endpoints/messaging/messages/create.js
rename to src/api/endpoints/messaging/messages/create.ts
index a88cc39ee..dbe7f617f 100644
--- a/src/api/endpoints/messaging/messages/create.js
+++ b/src/api/endpoints/messaging/messages/create.ts
@@ -3,8 +3,9 @@
 /**
  * Module dependencies
  */
-import * as mongo from 'mongodb';
+import it from '../../../it';
 import Message from '../../../models/messaging-message';
+import { isValidText } from '../../../models/messaging-message';
 import History from '../../../models/messaging-history';
 import User from '../../../models/user';
 import DriveFile from '../../../models/drive-file';
@@ -13,11 +14,6 @@ import publishUserStream from '../../../event';
 import { publishMessagingStream } from '../../../event';
 import config from '../../../../conf';
 
-/**
- * 最大文字数
- */
-const maxTextLength = 500;
-
 /**
  * Create a message
  *
@@ -29,55 +25,39 @@ module.exports = (params, user) =>
 	new Promise(async (res, rej) =>
 {
 	// Get 'user_id' parameter
-	let recipient = params.user_id;
-	if (recipient !== undefined && recipient !== null) {
-		if (typeof recipient != 'string') {
-			return rej('user_id must be a string');
-		}
+	const [recipientId, recipientIdErr] = it(params.user_id).expect.id().required().qed();
+	if (recipientIdErr) return rej('invalid user_id param');
 
-		// Validate id
-		if (!mongo.ObjectID.isValid(recipient)) {
-			return rej('incorrect user_id');
-		}
+	// Myself
+	if (recipientId.equals(user._id)) {
+		return rej('cannot send message to myself');
+	}
 
-		// Myself
-		if (new mongo.ObjectID(recipient).equals(user._id)) {
-			return rej('cannot send message to myself');
+	// Fetch recipient
+	const recipient = await User.findOne({
+		_id: recipientId
+	}, {
+		fields: {
+			_id: true
 		}
+	});
 
-		recipient = await User.findOne({
-			_id: new mongo.ObjectID(recipient)
-		}, {
-			fields: {
-				_id: true
-			}
-		});
-
-		if (recipient === null) {
-			return rej('user not found');
-		}
-	} else {
-		return rej('user_id is required');
+	if (recipient === null) {
+		return rej('user not found');
 	}
 
 	// Get 'text' parameter
-	let text = params.text;
-	if (text !== undefined && text !== null) {
-		text = text.trim();
-		if (text.length === 0) {
-			text = null;
-		} else if (text.length > maxTextLength) {
-			return rej('too long text');
-		}
-	} else {
-		text = null;
-	}
+	const [text, textErr] = it(params.text).expect.string().validate(isValidText).qed();
+	if (textErr) return rej('invalid text');
 
 	// Get 'file_id' parameter
-	let file = params.file_id;
-	if (file !== undefined && file !== null) {
+	const [fileId, fileIdErr] = it(params.file_id).expect.id().qed();
+	if (fileIdErr) return rej('invalid file_id param');
+
+	let file = null;
+	if (fileId !== null) {
 		file = await DriveFile.findOne({
-			_id: new mongo.ObjectID(file),
+			_id: fileId,
 			user_id: user._id
 		}, {
 			data: false
@@ -86,8 +66,6 @@ module.exports = (params, user) =>
 		if (file === null) {
 			return rej('file not found');
 		}
-	} else {
-		file = null;
 	}
 
 	// テキストが無いかつ添付ファイルも無かったらエラー
diff --git a/src/api/endpoints/messaging/unread.js b/src/api/endpoints/messaging/unread.ts
similarity index 100%
rename from src/api/endpoints/messaging/unread.js
rename to src/api/endpoints/messaging/unread.ts
diff --git a/src/api/endpoints/my/apps.js b/src/api/endpoints/my/apps.ts
similarity index 60%
rename from src/api/endpoints/my/apps.js
rename to src/api/endpoints/my/apps.ts
index 1f45a1a27..2466a47ce 100644
--- a/src/api/endpoints/my/apps.js
+++ b/src/api/endpoints/my/apps.ts
@@ -3,7 +3,7 @@
 /**
  * Module dependencies
  */
-import * as mongo from 'mongodb';
+import it from '../../it';
 import App from '../../models/app';
 import serialize from '../../serializers/app';
 
@@ -18,25 +18,12 @@ module.exports = (params, user) =>
 	new Promise(async (res, rej) =>
 {
 	// Get 'limit' parameter
-	let limit = params.limit;
-	if (limit !== undefined && limit !== null) {
-		limit = parseInt(limit, 10);
-
-		// From 1 to 100
-		if (!(1 <= limit && limit <= 100)) {
-			return rej('invalid limit range');
-		}
-	} else {
-		limit = 10;
-	}
+	const [limit, limitErr] = it(params.limit).expect.number().range(1, 100).default(10).qed();
+	if (limitErr) return rej('invalid limit param');
 
 	// Get 'offset' parameter
-	let offset = params.offset;
-	if (offset !== undefined && offset !== null) {
-		offset = parseInt(offset, 10);
-	} else {
-		offset = 0;
-	}
+	const [offset, offsetErr] = it(params.offset).expect.number().min(0).default(0).qed();
+	if (offsetErr) return rej('invalid offset param');
 
 	const query = {
 		user_id: user._id
diff --git a/src/api/endpoints/notifications/mark_as_read.js b/src/api/endpoints/notifications/mark_as_read.ts
similarity index 65%
rename from src/api/endpoints/notifications/mark_as_read.js
rename to src/api/endpoints/notifications/mark_as_read.ts
index 9c8a5ee64..6e75927cf 100644
--- a/src/api/endpoints/notifications/mark_as_read.js
+++ b/src/api/endpoints/notifications/mark_as_read.ts
@@ -3,10 +3,10 @@
 /**
  * Module dependencies
  */
-import * as mongo from 'mongodb';
-import Notification from '../../../models/notification';
-import serialize from '../../../serializers/notification';
-import event from '../../../event';
+import it from '../../it';
+import Notification from '../../models/notification';
+import serialize from '../../serializers/notification';
+import event from '../../event';
 
 /**
  * Mark as read a notification
@@ -17,16 +17,13 @@ import event from '../../../event';
  */
 module.exports = (params, user) =>
 	new Promise(async (res, rej) => {
-		const notificationId = params.notification;
-
-		if (notificationId === undefined || notificationId === null) {
-			return rej('notification is required');
-		}
+		const [notificationId, notificationIdErr] = it(params.notification_id).expect.id().required().qed();
+		if (notificationIdErr) return rej('invalid notification_id param');
 
 		// Get notification
 		const notification = await Notification
 			.findOne({
-				_id: new mongo.ObjectID(notificationId),
+				_id: notificationId,
 				i: user._id
 			});
 
diff --git a/src/api/it.ts b/src/api/it.ts
index f4b28531d..039f87995 100644
--- a/src/api/it.ts
+++ b/src/api/it.ts
@@ -424,7 +424,7 @@ class IdQuery extends QueryCore {
 	/**
 	 * このインスタンスの値およびエラーを取得します
 	 */
-	qed(): [any[], Error] {
+	qed(): [mongo.ObjectID, Error] {
 		return super.qed();
 	}
 
@@ -433,7 +433,7 @@ class IdQuery extends QueryCore {
 	 * バリデータが false またはエラーを返した場合エラーにします
 	 * @param validator バリデータ
 	 */
-	validate(validator: Validator<any[]>) {
+	validate(validator: Validator<mongo.ObjectID>) {
 		return super.validate(validator);
 	}
 }
diff --git a/src/api/models/messaging-message.ts b/src/api/models/messaging-message.ts
index cad6823cb..50955d7fb 100644
--- a/src/api/models/messaging-message.ts
+++ b/src/api/models/messaging-message.ts
@@ -1,3 +1,8 @@
 import db from '../../db/mongodb';
 
 export default db.get('messaging_messages') as any; // fuck type definition
+
+export function isValidText(text: string): boolean {
+	return text.length <= 1000 && text.trim() != '';
+}
+
diff --git a/src/api/serializers/messaging-message.ts b/src/api/serializers/messaging-message.ts
index 4a4c8fc5b..da63f8b99 100644
--- a/src/api/serializers/messaging-message.ts
+++ b/src/api/serializers/messaging-message.ts
@@ -19,7 +19,7 @@ import deepcopy = require('deepcopy');
  */
 export default (
 	message: any,
-	me: any,
+	me?: any,
 	options?: {
 		populateRecipient: boolean
 	}