When a first one-way traffic road becomes partially impassable because of roadworks, a second one-way traffic road temporarily replaces the first road and is used in a direction opposite to an original trafficable direction. This second road is registered as a replacing road based on traffic information from the VICS center. When the second road registered as the replacing road is present within a given area surrounding the current position of a relevant vehicle, map matching is executed without considering the original trafficable direction of the second road. This allows the second road to be designated as a travel road through the map matching even when the relevant vehicle travels in a direction opposite to the original trafficable direction of the second road.