An in-vehicle arithmetic unit calculates a required time, which is needed for a vehicle to arrive at a traffic light when the vehicle maintains a present speed, according to a speed of the vehicle, a present position of the vehicle, and information on the traffic light. An in-vehicle determination unit determines whether the vehicle can pass the traffic light by maintaining the present speed, according to the required time and the traffic light information. An in-vehicle generating unit generates a request signal to request the traffic light to light a passing permission color such as a blue light after the required time elapses, in response to a determination that the vehicle cannot pass the traffic light. An in-vehicle transmission unit transmits the request signal to the traffic light. A control unit of the traffic light controls the signal light according to the transmitted request signal.