diff --git a/app.js b/app.js
new file mode 100644
index 0000000..b2de61d
--- /dev/null
+++ b/app.js
@@ -0,0 +1,23 @@
+const express = require('express');
+const http = require('http');
+const socketIo = require('socket.io');
+
+const app = express();
+const server = http.createServer(app);
+const io = socketIo(server);
+
+// このように書くことで`public/script.js`にアクセスできる
+app.use(express.static('websocket'));
+
+io.on('connection', (socket) => {
+  socket.on('chat message', (msg) => {
+    io.emit('chat message', msg);
+  });
+});
+
+const PORT = 3000;
+
+server.listen(PORT, () => {
+  console.log(`Server is running on http://localhost:${8888}`);
+});
+