PURPOSE: To accurately detect the objective traveling azimuth irrespective of distortion or secular changes of terrestrial magnetism by a detector wherein traveling azimuth of a moving body is computed based on the value corrected from the updated data on a moved amount of the origin and gain data for correcting to a real circle.

CONSTITUTION: An azimuth detecting section 1 detects azimuth of terrestrial magnetism with components decomposed in the X and Y directions and, upon command of 1-rotation correction from timing means 3, gain computing means 21 determines gain data with which vector locus described by an electric signal in the X and Y directions is made a real circle. Anomaly decision means 22 applies the detected signal to origin movement computing means 23 when it has decided that the electric signal in the X and Y directions from the detecting section 1 is not at an anomalous level. The means 23 stores the electric signal and determines a moved amount of the origin as origin movement data. When the electric signal in the X and Y directions from the detecting section 1 is inputted to azimuth computing means 24, it is corrected to such a value as locating on a vector locus of real circle about the origin based on data from both means 21, 23. This corrected value is used to compute the traveling azimuth of a moving body.