Power supply of ECUs connected to a communication network is optimally controlled so that power consumption is reduced. A transceiver/receiver converts a message of a differential signal received via a CAN bus into a digital signal. A select circuit determines whether the converted message is in a CAN format or a UART format. If it is in the UART format, the select circuit outputs a message to the UART circuit. A UART circuit determines whether the message matches a UART format. If matched, an ID determination circuit determines whether the input message is specifying a CAN ID of its own ECU. If it is the CAN ID of the ECU, the ID determination circuit outputs an enable signal to turn on a regulator and supply power to an MCU and an actuator.