A map update data supply apparatus includes: isolation detection means (8) for detecting the presence and the absence of an isolated state in which some of the roads are isolated from other roads in a road network of target map data due to updating of one or more update target segments of the target map data based on update map data (Ma); extraction means (9) for extracting, as update required segments, segments of the update map data (Ma), other than the update target segments, that have a road that connects to the isolated some of the roads when it is detected that there is the isolated state; and update data file generating means (10) for generating update data files (fa) for the update target segments and the update required segments based on the update map data (Ma).