A vehicular navigation system includes: a current position detection unit for detecting the current position of the vehicle; an information storage unit for storing map information for conducting route searching and for providing route guidance; an input unit for inputting a destination and inputting instructions for executing a search of the map information for a route from the current position detected by the current position detection unit to the destination; an output unit for outputting information for route guidance; and a central processing unit for temporarily memorizing a route detected by the route search and for outputting a signal to the output unit to provide route guidance according to the memorized route. The central processing unit judges whether or not one information storage unit has been replaced by another and, when replaced, if the destination has not been reached, conducts another route search from the current position to the destination.