A roadside communicator in a roadside around an intersection transmits, to vehicles around the intersection, traffic light information on traffic light at the intersection and mobile object information on vehicles and pedestrians around the intersection. An in-vehicle communicator mounted in a subject vehicle acquires the traffic light information and the mobile object information. An in-vehicle engine start determination section mounted in the subject vehicle determines a permission or prohibition of a start of an engine of the subject vehicle based on the traffic light information and mobile object information. The engine start determination section determines an engine start time in consideration of a display of the traffic light, and states of mobile objects that pass through the intersection. An in-vehicle engine control section in the subject vehicle starts the engine when the engine start determination section permits the start of the engine.