A map data processing unit includes a batch update section and dynamic update section. A type of update data fed from an update data input section is decided using header information. If the update data is route search data, the batch update section collectively updates all the map data to latest version map data according to the update data from the update data input section. If the update data is not the route search data, the dynamic update section updates the map data to the latest version map data according to the update data every time the map data becomes necessary. Thus performing the collective or dynamic update according to the type of the update data enables the update to the latest map data without affecting the operation speed of a navigation function, with minimizing the time precluding the use of the navigation function.