A server in an information base determines a route (server route) from a place of departure to a destination, transmitted from a client terminal of a navigation unit via communication, using information in a server database. On the other hand, the client terminal determines a route (client route) from the place of departure to the destination using information in a client terminal database. Either the server or the client terminal determines whether or not the server route and the client route are identical based on information concerning guiding points of each route, and the client terminal then performs route navigation of a route in a section where the routes are identical using the information in the client terminal database and a route in a non-identical section where the routes are not identical using the information in the server database. In this way, the information in the client terminal database is effectively used in the route navigation and thereby an amount of information to be transmitted to the client terminal from the server is decreased.