To measure the bearing of a moving body, e.g. head bearing, etc., of a work ship at a high accuracy even if using a compass having a comparatively low bearing measuring accuracy such as magnetic compass, etc.

A reference antenna A1 and measuring antenna A2 are disposed with a specified interval, the bearing of a moving body (head bearing of a work ship) is measured by a magnetic compass, the calculated double phase difference of the carrier phases at the two antennas' positions is obtd. from the interval between the two antennas, bearings thereof and positions of a plurality of GPS satellites, the observed double phase difference of the carrier phases at the two antennas' positions is obtd. from radio waves received from the plurality of GPS satellites by the two antennas, the calculated double phase difference is corrected so as to coincide with the decimal part of the observed double phase difference in a range of ±0.5 cycles, thereby obtaining the relative position of the measuring antenna to the reference antenna at a high accuracy and the bearing of the moving body is obtd. from the relative position relation of both at a high accuracy.