Navigation system

A navigation system is provided with: a present position detecting device (1) for detecting a present position of a movable body; a reading device (14) for reading map data recorded on a recording medium (1); a nonvolatile storage device (15) for storing the map data thereon; a selecting device (11) for selecting an area as an object to be transmitted in accordance with the present position; a transmitting device (11) for reading the recorded map data corresponding to the area from the recording medium (1) and transmitting the read map data to the nonvolatile storage device (15) at a predetermined timing; and a controlling device (11) for controlling a navigation operation to assist the movable body in traveling on the basis of the recorded map data on the recording medium (1) and the stored map data on the nonvolatile storage device (15).