Navigation device and map data product

A navigation device includes: a storage unit 13 that stores map data divided into a plurality of files for a predetermined map range; an acquisition unit 10 that acquires map updating data for updating the map data; an extraction unit 10 that extracts at least one file from among the map data files; and an updating unit that updates the map data by storing new map data files based upon the map updating data in the storage unit, after having deleted the map data files from the storage unit 13 with the exception of the file extracted by the extraction unit 10.