A positional information acquiring unit acquires positional information of a vehicle. An intersection predicting unit predicts an intersection, which the vehicle will enter, by associating the positional information with map information. An entrance predicting unit acquires the positional information of another vehicle included in a packet signal from a transmitting apparatus mounted on the other vehicle and associates the positional information of the other vehicle with the map information, thereby predicting whether the other vehicle enters the intersection predicted by the intersection predicting unit. When entrance of the other vehicle is predicted, an effect predicting unit predicts whether travel of the other vehicle has an effect on this vehicle based on traveling direction information of the other vehicle acquired from the packet signal. The notifying unit notifies presence of the other vehicle when presence of the effect is predicted.