To provide an on-board network system capable of preventing reception failure of control data to be delivered to a communication bus with minimum changes in the configuration of each ECU.

A keyless entry system enables a verification ECU 20 to deliver keyless data to a communication bus at the lapse of a control time T1 after the delivery of a startup signal and enables a door ECU 30 and a light ECU 40 to complete wake-up processing at each of return standby time Ty(<T1), Tz(>T1) after the detection of the startup signal, so that a power saving state is returned to an ordinary state. In addition, the system includes a data relay device 50 which retains keyless data delivered to the communication bus upon completion of the wake-up processing at the return standby time Tx(<T1) and which delivers the keyless data to the communication bus at a standby time T2 after the completion of the wake-up processing. Thus, a light ECU 40 can receive keyless data from the data relay device 50.