The present invention provides, in a car navigation system, a unit of notifying a user of the update contents of map data prior to the downloading of the map data. A vehicle-mounted terminal sets a difference update area in accordance with a selection made by a user and sends a difference update request to a map updating server. If an update mode in this case is "update after outline display", the vehicle-mounted terminal downloads an outline update map from the map updating server. The outline update map is displayed on a display unit of a display. Here, when a download start button displayed on the display unit is depressed, the vehicle-mounted terminal downloads a detailed update map from the map updating server. The detailed update map is then displayed on the display unit of the display. Furthermore, an updating process is performed on the map data stored in a terminal DB.