PURPOSE: To confirm the presence or absence of its current position in a traffic data on the map referring to the measured location data and, when it is absent, to indicate its own position with the measured location data instead of the matched location data during a specified time or running distance.

CONSTITUTION: When own vehicle is judged to be running on a road registered in a traffic data, a system controller 5 matches the traffic data from a CD-ROM drive 12 with a self position data based on the data from an earth magnetism sensor 1, angular velocity sensor 2 and running distance sensor 3, or the measured data from a GPS receiver 4. Then it judges whether or not a lead-in distance is more than a specified value, and if it is so, the vehicle is judged to be running on a road not registered in the traffic data. If it is below the specified value, it is judged in a same manner whether or not a lead-in angle is more than a specified value, and if it is so, own current position obtained through measuring position is indicated. Thus, even during running on the road not registered in the traffic data, the current position can be indicated more precisely.