A mobile-body navigation system comprises; a navigation apparatus that is disposed in a mobile body and includes a position detection portion for detecting a position of the mobile body, a transmitter-receiver portion, a processing portion, a display portion, and a storage medium; a radio communication apparatus for carrying out interactive radio communication with the transmitter-receiver portion; and a server apparatus that includes a map information database; wherein the server apparatus repeats extraction of high-priority map information for map display from the map information database based on a mobile-body position that is detected by the position detection portion and received via the transmitter-receiver portion and via the radio communication apparatus, and repeats transmission of the extracted map information to the transmitter-receiver portion via the radio communication apparatus, the processing portion receives the map information via the transmitter-receiver portion, makes the storage medium store the received map information, and makes the display portion display a map based on the stored map information and on the mobile-body position detected by the position detection portion.