A road zone assessment device has a processor configured to select a first road zone from among multiple first road zones representing a first road associated with a vehicle navigation route, and connected with a second road zone representing a second road different from the first road, on a location-estimating map used for a vehicle, to determine whether or not the navigation route extends from the selected first road zone to the second road zone, to identify other first road zone associated with the navigation route from the selected first road zone forward on the destination location side of the navigation route, and to release association between the other first road zone and the navigation route when the selected first road zone is connected with the second road zone and the navigation route extends from the selected first road zone to the second road zone.