Before a communication control device ECU falls into a sleep state or a power-off state, a substitution request is transmitted to an ECU, among substitute candidate devices ECU to ECU, that is determined by a substitute transmission acceptability determining unit as being capable of taking over the communication control device. A substitution-capable processing load quantity, a substitution-capable process importance level, or a failure determination result of each of the ECUs is used as determination criteria when the substitute transmission acceptability determining unit of the ECU determines a substitute device, and the determination is carried out in an order that takes into consideration the process importance level of each of the ECUs during travelling or at a standstill, to prevent failures in a network or abnormal behaviors of a vehicle.
Control device switching system