To surely register codes to be registered from a remote place without registering wrong codes.

A write mode in which a characteristic mode is written into an E2PROM is started on a command from a writing device (200, 202), and a write permission code is set by setting the registration frame of the E2PROM according to the registration number designated (204 to 212). When the write permission mode set is received from an ignition key (214), the characteristic code received is registered according to the registration number (218 to 224). Therefore, since only the preset write permission code is permitted, the characteristic code involved in the wave transmitted from adjacent processes is not registered on the E2PROM as a normal characteristic code by mistake.