Navigation system

A first navigation system is provided with: a present position detecting device (16, 17) for detecting a present position; a plurality of memory devices (14, 15) each capable of reading out map data which is recorded therein; a navigation controlling device (11) for controlling a navigation operation in correspondence with the detected present position by using the map data; and a map data reading device (11) for accessing one of the memory devices, which is selected in accordance with a predetermined condition, and reading out the map data required for the navigation operation therefrom.