diff --git a/src/api/common/watch-post.ts b/src/api/common/watch-post.ts
new file mode 100644
index 000000000..9f5e7a913
--- /dev/null
+++ b/src/api/common/watch-post.ts
@@ -0,0 +1,21 @@
+import * as mongodb from 'mongodb';
+import Watching from '../models/post-watching';
+
+export default async (me: mongodb.ObjectID, post: mongodb.ObjectID) => {
+	// if watching now
+	const exist = await Watching.findOne({
+		post_id: post,
+		user_id: me,
+		deleted_at: { $exists: false }
+	});
+
+	if (exist !== null) {
+		return;
+	}
+
+	await Watching.insert({
+		created_at: new Date(),
+		post_id: post,
+		user_id: me
+	});
+};
diff --git a/src/api/endpoints/posts/polls/vote.ts b/src/api/endpoints/posts/polls/vote.ts
index d359d7d2c..7bd9119fc 100644
--- a/src/api/endpoints/posts/polls/vote.ts
+++ b/src/api/endpoints/posts/polls/vote.ts
@@ -4,7 +4,9 @@
 import $ from 'cafy';
 import Vote from '../../../models/poll-vote';
 import Post from '../../../models/post';
+import Watching from '../../../models/post-watching';
 import notify from '../../../common/notify';
+import watch from '../../../common/watch-post';
 import { publishPostStream } from '../../../event';
 
 /**
@@ -75,6 +77,32 @@ module.exports = (params, user) => new Promise(async (res, rej) => {
 		post_id: post._id,
 		choice: choice
 	});
+
+	// Fetch watchers
+	Watching
+		.find({
+			post_id: post._id,
+			user_id: { $ne: user._id },
+			// 削除されたドキュメントは除く
+			deleted_at: { $exists: false }
+		}, {
+			fields: {
+				user_id: true
+			}
+		})
+		.then(watchers => {
+			watchers.forEach(watcher => {
+				notify(watcher.user_id, user._id, 'poll_vote', {
+					post_id: post._id,
+					choice: choice
+				});
+			});
+		});
+
+	// この投稿をWatchする
+	// TODO: ユーザーが「投票したときに自動でWatchする」設定を
+	//       オフにしていた場合はしない
+	watch(user._id, post._id);
 });
 
 function findWithAttr(array, attr, value) {
diff --git a/src/api/endpoints/posts/reactions/create.ts b/src/api/endpoints/posts/reactions/create.ts
index ba5b69ada..7cae3830e 100644
--- a/src/api/endpoints/posts/reactions/create.ts
+++ b/src/api/endpoints/posts/reactions/create.ts
@@ -4,7 +4,9 @@
 import $ from 'cafy';
 import Reaction from '../../../models/post-reaction';
 import Post from '../../../models/post';
+import Watching from '../../../models/post-watching';
 import notify from '../../../common/notify';
+import watch from '../../../common/watch-post';
 import { publishPostStream } from '../../../event';
 
 /**
@@ -84,4 +86,30 @@ module.exports = (params, user) => new Promise(async (res, rej) => {
 		post_id: post._id,
 		reaction: reaction
 	});
+
+	// Fetch watchers
+	Watching
+		.find({
+			post_id: post._id,
+			user_id: { $ne: user._id },
+			// 削除されたドキュメントは除く
+			deleted_at: { $exists: false }
+		}, {
+			fields: {
+				user_id: true
+			}
+		})
+		.then(watchers => {
+			watchers.forEach(watcher => {
+				notify(watcher.user_id, user._id, 'reaction', {
+					post_id: post._id,
+					reaction: reaction
+				});
+			});
+		});
+
+	// この投稿をWatchする
+	// TODO: ユーザーが「リアクションしたときに自動でWatchする」設定を
+	//       オフにしていた場合はしない
+	watch(user._id, post._id);
 });
diff --git a/src/api/models/post-watching.ts b/src/api/models/post-watching.ts
new file mode 100644
index 000000000..41d37e270
--- /dev/null
+++ b/src/api/models/post-watching.ts
@@ -0,0 +1,3 @@
+import db from '../../db/mongodb';
+
+export default db.get('post_watching') as any; // fuck type definition