A navigation device comprising: a map database for storing a plurality of map data divided into predetermined update units, said update units corresponding to map sections defined by distance or area, the update units respectively include identification information indicating an identification symbol for identifying each of the update units and version information indicating a present update version; receiving means for receiving, via a communication network, update data generated for each of the update units, wherein the update data include; difference information indicating an update content of update subject map data as a difference with pre-update map data, identification information indicating the identification symbol of the update subject map data, and version information indicating a post-update update version; reading means for reading the update data from a recording medium storing a plurality of the update data; and updating means for performing a differential update on the map data stored on the map database using the update data received by the receiving means and then using the update data read by the reading means, wherein, the updating means is adapted for, when performing the differential update on the map data stored on the map database using the update data read by the reading means, extracting for each of the update units the update data having identification information that matches the identification information of the map data and having a later update version, than the update version of the map data from the plurality of the update data stored on the recording medium, and performing the differential update on the map data using the extracted update data. a map database for storing a plurality of map data divided into predetermined update units, said update units corresponding to map sections defined by distance or area, the update units respectively include identification information indicating an identification symbol for identifying each of the update units and version information indicating a present update version; receiving means for receiving, via a communication network, update data generated for each of the update units, wherein the update data include; difference information indicating an update content of update subject map data as a difference with pre-update map data, identification information indicating the identification symbol of the update subject map data, and version information indicating a post-update update version; difference information indicating an update content of update subject map data as a difference with pre-update map data, identification information indicating the identification symbol of the update subject map data, and version information indicating a post-update update version; reading means for reading the update data from a recording medium storing a plurality of the update data; and updating means for performing a differential update on the map data stored on the map database using the update data received by the receiving means and then using the update data read by the reading means, wherein, the updating means is adapted for, when performing the differential update on the map data stored on the map database using the update data read by the reading means, extracting for each of the update units the update data having identification information that matches the identification information of the map data and having a later update version, than the update version of the map data from the plurality of the update data stored on the recording medium, and performing the differential update on the map data using the extracted update data.