To measure an azimuth angle with high precision by using a geomagnetic sensor.

An orthogonal magnetic detecting coil decomposes a horizontal component of a terrestrial magnetic field into two components of a voltage output signal to be detected. Then the voltage output signal is input to a microcomputer 23 having a signal calibration computing means. An azimuth data regarding geomagnetic north is computed and output by a geomagnetic sensor 20. In this azimuth measuring system using the geomagnetic sensor 20, a correction processing means 10 calculates correction values for all the azimuth data from the microcomputer 23, and adds the correction values to the aforesaid azimuth data. The correction processing means 10 is attached to the microcomputer 23 in this system.