To obtain the more proper error of the oscillation frequency.

The moving direction and the velocity are calculated as the satellite information based on the GPS (Global Positioning System) signals. Based on the calculated satellite information and the imparted presumed actual position, the presumed position standard Doppler shift amount is calculated. Based on the receiving frequencies of the GPS signals for every of the plurality of GPS satellites and the presumed position standard Doppler shift amount, the oscillation frequency errors are calculated.