A user operates a remote control to enter an authentication code shared by a plurality of radio transmission devices performing radio transmission. Remote control transmission/reception unit 1 converts an infrared signal received from the remote control to an electric signal, and extracts the authentication code from the electric signal. The authentication code is recorded on an authentication code record region in a nonvolatile storage region. In an authentication communication mode, a radio unit encrypts a radio unit MAC address with the authentication code used as a key, and transmits it. Further, the radio unit decrypts the radio unit MAC address returned from the radio transmission device of the opposite party of the transmission with the authentication code used as the key. The radio transmission device obtains the radio unit MAC address of the opposite party of the transmission, and ends the authentication mode.