A group of maps corresponding to the present position detected by a position detection unit is retrieved from a storage unit. Also, a map on the same scale as a map being displayed is extracted from the retrieved group of maps. If there is an overlapped portion between the extracted map and the map being displayed, they are displayed with the overlapped portion held. With this, both the map being displayed and the extracted map can be displayed as if they were continuous to each other, and the present-position mark can be displayed without being jumped considerably.