A roadside device transmits, to a server, detection information indicating a detection result from a roadside sensor. In a case that a vehicle moving on a road toward the roadside device reaches a notification start point and that the vehicle is in a first geographic range, the server transmits the detection information received from the roadside device to the vehicle via the communication network. In a case that the vehicle moves from the first geographic range to a second geographic range located closer to the roadside device than the first geographic range, the roadside device transmits the detection information to the vehicle by the wireless communication.