When a navigation system is started for the first time, a time/position information item unique to each navigation system is generated based on a position and time detected for the first time by a GPS receiver of a position detector. This generated time/position information item is stored both in a hard disk of a map data storage device and in an internal memory. When a starting process performed at starting of the system, it is determined whether time/position information items stored in the hard disk and the internal memory accord with each other. When both information items are determined to be according with each other, map data stored in the hard disk is given a license for use.