PURPOSE: To exactly detect and confirm the present position of a moving body by using a beacon radio wave, when it has been decided that there are three pieces of usable artificial satellites.

CONSTITUTION: When it is decided that there are three pieces of artificial satellites which can receive a radio wave, whether a beacon radio wave has been received or not is decided by a beacon reception deciding part 43 in a data processing/communication control part 41. In this case, when it has been decided to be YES, accordingly, based on the contents of a radio wave signal by which the beacon radio wave has been received from a beacon use antenna 11 to a beacon receiving part 12, a two-dimensional coordinate data against the present position of a moving body is obtained. Subsequently, based on the two-dimensional data obtained in such a way, and a position measuring data due to a fact that a GPS satellite radio wave has been received, the altitude of the moving body is calculated. The obtained altitude data is stored in a data storage part 5.