To provide a technique for properly determining whether vehicle information memorized in an on-vehicle device really corresponds to a vehicle on which the on-vehicle device should be mounted.

A frame number is memorized in a memory 25 in an engine ECU20 during manufacturing of a vehicle. At the time of vehicle registration, an automobile registration number and the frame number read from a secondary code written in an automobile inspection certificate by a handy terminal 30 are transmitted to an electronic license plate 10. The electronic license plate 10 writes those number in a memory 15 and transmits that to the engine ECU. The engine ECU memorizes the automobile registration number received from the electronic license plate 10 in the memory 25, when the frame number received from the electronic license plate 10 watches with the frame number memorized in the memory 25. In an IG on state, it is determined whether the automobile registration number and the frame number read out from the memory 25 of the engine ECU 20 match with the automobile registration number and the frame number read out from the memory 15 of the electronic license plate 10.