PURPOSE: To improve the accuracy of the titled apparatus and to make it possible to use the same even in the polar regions, by calculating a stem azimuth from the azimuth of a GPS satellite with respect to the stem azimuth obtained by detecting the phase difference of the cycle of the phase change of the received radio wave from the GPS satellite and a cylce for successively changing over antenna and the azimuth of the GPS satellite obtained from a GPS receiver.

CONSTITUTION: In a place detector 42, the phase difference of the output of a changed-over wave generator 44 and the output of a second band pass filter 40 is taken out and the signal thereof is subsequently introduced into the one input terminal of a stem azimuth operator 46. On the other hand, the azimuth signal of a GPS satellite containing the PN code of a GPS receiver 48 is supplied to the other input terminal of the stem azimuth operator 46. As a result, in the operator 46, operation is performed so as to subtract the output of the phase detector 42+(90°-360°/16) and, therefore, the stem azimuth is calculated to be displayed by a display device 50.