PURPOSE: To prevent the generation of a traffic accident based on a jump phenomenon, by neglecting a GPS data which has been obtained at some time point, when the GPS data at some time point exceeds a GPS data at the time point immediately before it.

CONSTITUTION: A difference is taken between a whole world position measuring system GPS data at some time point, and GPS data immediately before, which is obtained immediately before said data and has been stored temporarily in a GPS data storage device 63, and whether its result enters into a prescribed range or not is decided by a compatator 62. When a result of its decision is YES, its own present position is displayed, based on the GPS data being a satellite data. On the other hand, when a result of its decision is NO, its own present position is displayed, based on a self-standing type data. In such a way, the generation of the jump phenomenon is prevented surely, and it does not occur that the present position is misconceived.