In map data having link information, each of the links has reference information regarding a start point node of the link, a next link in a series of links, and an upper link. Further, links are memorized in a form of link list, and the position of the link in the link list is not changed in the course of adding/deleting a link, thereby enabling a direct reference to each of the links in the link list by the position of the link. The link information organized in the above-described manner enables the ease of the update of the map data as well as the speed-up of the calculation of, for example, a navigation route.