To decrease the time taken to determine whether or not route guide should be restarted after power down.

This method detects the power down of a vehicle, and in response to this determines whether or not route guide may be restarted in response to the next startup of the vehicle. This determination is made prior to the power down of a system 1 according to the current position of the vehicle and the route calculated. If the determination to restart the guide after startup is made, the destination selected and the route calculated are saved in memories 11, 12 before the power down of the system 1. Next, the destination selected and the calculated route of the vehicle are read from the memories 11, 12 in response to the next startup of the vehicle, and the route guide is restarted from the current position of the vehicle.