1. A map data update method for updating nationwide updated version map data using route-specific update data, comprising the steps of: creating route-specific update data, comprising update data for all routes which have been newly opened since the time of release of the nationwide updated version map data; storing a plurality of the route-specific update data sets with different creation dates; when updating the nationwide updated version map data of the time of release, stored in a navigation apparatus, in use of a stored prescribed first route-specific update data, storing pre-update map files necessary to restore the nationwide updated version map data; and updating the nationwide updated version map data using the first route-specific update data.