1. A map update data supply device for supplying data for updating a map database to a navigation device that has the map database, the map database including at least road network information and is divided into a plurality of sections, the map update data supply device comprising: an update map database for managing per section versions of an update data file for difference updating a map database, and for storing per section versions of the update data file; a request update data extraction unit that, based on an update request from a navigation device, is configured to extract a request update section subjected to a difference update, and for each request update section, the request update data extraction unit is configured to extract and supply, to the navigation device, an update data file up to the latest version of the update data file; a safeguard update data extraction unit that, if all the request update sections are updated up to the latest version, the safeguard update extraction unit is configured to extract a safeguard update section to safeguard a road network connection between adjacent sections, the safeguard update data extraction unit being configured to extract, for each safeguard update section, the update data file up to an update safeguard version, wherein the update safeguard version is a version requiring an update in order to safeguard the road network connection; an integrated data generation unit for integrating, per request update section, all versions up to the latest version of the update data file for each request update section extracted by the request update data extraction unit, the integrated data generation unit configured to generate a request update integrated data file that serves as a data file for one difference update, and the integrated data generation unit further configured to integrate per safeguard update section, versions of the update data file up to the update safeguard version for each safeguard update section extracted by the safeguard update data extraction unit, the integrated data generation unit configured to generate a safeguard update integrated data file as a data file for one difference update; and an integrated data supply unit for supplying, to the navigation device, the request update integrated data file and the safeguard update integrated data file generated by the integrated data extraction unit.