PURPOSE: To measure continuously a position without any break by estimating the position by using azimuth data and range data from a magnetic goniometer and a range finder and position measurement data right before the interruption of reception.

CONSTITUTION: When a radio wave from a GPS (global positioning system) satellite is cut off by a shield and its reception is interrupted, an estimated position computing element 2 receives a position measurement failure alarm signal sent out of a GPS receiver 1 and starts operating to estimate the position until the reception is restarted on the basis of the azimuth data and range data from the magnetic goniometer 7 and range finder 8 and the measured position right before the transmission of a position measurement failure alarm of a receiver 1. This estimated position information is outputted to a position display device 4 through a data switch 3 which is operated to the side of the computing element 2 with the position measurement failure alarm signal outputted from the receiver 1, so that the information is displayed numerically. When the receiver 1 restarts the reception and begins to measure the position, the switch 3 is changed over to the side of the receiver 1 and the display device 4 displays the position measurement result of the receiver 1.