A system includes a first device and a second device connected via an on-board network. In a case where a driving assistance function is selectively installed on a vehicle, the first device transmits repeatedly a CAN frame having a predetermined CAN-ID from start of the vehicle to stop of the vehicle. The second device receives a CAN frame having a CAN-ID uniquely set for a function with regard to the vehicle. And the second device is configured to: (i) record to both a first recording region and a second recording region of a memory in a case where it is determined that the CAN-ID included in the received CAN frame is the predetermined CAN-ID; and (ii) record only to the second recording region in a case where it is not determined that the CAN-ID included in the received CAN frame is the predetermined CAN-ID.