PURPOSE: To provide certainty and correctness by performing a relative-mode position-detecting process, and, if it is difficult to estimate a reliable position, switching the process to an absolute-position detecting process, and performing that relative-mode position-detecting process which corresponds to the absolute mode.

CONSTITUTION: The system comprises a base station, a support station, a key station, a vehicle station and a storage medium. The vehicle station has a position detecting device and a road-information storage medium, etc. An area is detected by the position detecting device and specified according to its latitude and longitude, and a relative mode is started by an index from the number of the area, and navigation is carried out in the relative mode according to data on travel. Guidance from the key station is also processed in the relative mode and routes are displayed in sequence by the painting out of the corresponding nodes. An absolute-mode position detecting process is carried out as navigation is carried out in the relative mode, and in the case of the shift into a movable area which is not recorded on the storage medium for map information and the like, it is announced and the displaying of routes in the relative mode is switched to that in the absolute mode.