When a corridor operation is conducted in a car navigation system, a stoppable place where a vehicle is able to stop is retrieved before a map disk is removed. The stoppable place is a place that is located along a route to a destination and also as close as possible to a regional boundary of map data clipped out from the map disk to an external memory. When the stoppable place is retrieved, route guiding is performed so that the retrieved stoppable place is regarded as a temporary destination. Therefore, re-setting the map disk can be safely achieved by stopping the vehicle at the stoppable place, which helps prevent usability of the corridor operation from deteriorating.