PURPOSE: To utilize the range of GPS position measurement precision effectively and to detect the current position of a vehicle with improved correctness.

CONSTITUTION: A GPS receiver 10 is provided with a DOP specifying element 11 for specifying the GPS position measurement precision, a satellite combination determining element 12 and a satellite combination specifying element 13 for selecting satellites of specified DOP, and a satellite signal receiving element 14 and an absolute position calculating element 15 for calculating the absolute position of a vehicle by utilizing radio wave signals received from the selected satellites. On the other hand, a driver's own vehicle position determining element 20 is provided with a current place estimating element 21 having an azimuth sensor 31 and a distance sensor 32 connected therefor and realizing dead reckoning, a GPS use determining element 23 and a DOP specifying element 24 for relaxing the specification of DOP when the combination of the satellites of the specified DOP is not present, and a comparing element 22 for comparing GPS for which the specification of the DOP is relaxed with the dead reckoning and selecting the one having a smaller error.