A near field communication (NFC) sticker which stores a key is attached to a new client device. A remote commander in a home network reads the key using a NFC interface and IR-transmits it to a home network server. Once the client is connected to the network, it encrypts its own device information with the key and sends the encrypted information to the server, which decrypts the data with the key sent from the remote commander. In this way, client device registration is executed easily and securely.