A GPS position-measuring device includes a altitude-information memory for storing altitude information of a moving object, a combination determining unit for determining GPS-satellite combinations from GPS satellites that can be tracked, a position measuring unit for measuring a GPS based or GPS derived three-dimensional position of the moving object for each GPS-satellite combination, and a difference extracting unit for determining a difference in altitude between GPS derived altitude information contained in the measured GPS related three-dimensional position and the altitude information supplied from the altitude-information memory. The GPS position-measuring device further includes a position determining unit for comparing the extracted difference in altitude with a threshold value, selecting a GPS-satellite combination with which the difference in altitude is less than or equal to the threshold value, and determining a measurement position of the moving object based on the GPS derived three-dimensional position of the selected GPS-satellite combination.