When a vehicle passes through a predetermined spot, a vehicle control device sends a transmission signal including a vehicle number counter set to an initial value in a rearward direction of the vehicle. When the transmission signal is received through the inter-vehicle communication module from a vehicle that leads the own vehicle, the vehicle control device sets the vehicle number counter included in the transmission signal, to an updated value resulting from increasing the vehicle number counter by a predetermined value, and sends a transmission signal including the vehicle number counter set to the updated value in the rearward direction of the vehicle. The vehicle control device sends the vehicle number counter set to the initial value or the updated value, to a center server, if it is determined that there is no vehicle that follows the own vehicle at a relatively short inter-vehicle distance.