Unpossessed road data is added to possessed road data stored in a road contour database of an information center. An on-vehicle terminal apparatus first compares a current position of a vehicle detected by a D-GPS unit against the road data stored in a storage section for storing road contour data of possessed roads. If the current position deviates from a known existing road, it is determined that the vehicle travels on an unpossessed road. Road data of the unpossessed road is then obtained based on a travel locus of the vehicle and sent to the information center together with a reliability index of the road data. The information center collects unpossessed road data from a plurality of sources, evaluates the reliability index for each data, and adds sufficiently reliable road data to the possessed road data. Thus, the information center can quickly obtain and utilize new and reliable road data.