A position calculating apparatus that calculates a position of a moving body by using results of positioning by a GPS satellite and a self-contained sensor includes receiving means for receiving GPS orientation data measured by the GPS satellite and navigation orientation data measured by the self-contained sensor; first determining means for determining a reliability of the GPS orientation data; second determining means for determining a reliability of the navigation orientation data; and movement angle calculating means for calculating a movement angle of the moving body from the GPS orientation data or the navigation orientation data in accordance with the determination results of the first and second determining means.