After a request for first data is received from a first diagnostic unit, when a request for second data is received from a second diagnostic unit, if the first data and the second data of the same type, then a communication unit requests the electronic control unit to send the same type of data, and sends the same type of data received from the electronic control unit to the first diagnostic unit and the second diagnostic unit. If the first data and the second data are of different types, then the communication unit requests the electronic control unit to send the first data and the second data, receives the first data and the second data all together from the electronic control unit, sends the received first data to the first diagnostic unit, and sends the received second data to the second diagnostic unit.