PURPOSE: To reduce the required measuring time while simplifying the operation eliminating intial state procedure by controlling a torque unit from a declination and a time differentiation to rest a gyro section.

CONSTITUTION: A gyro rotor 1 is suspended on a body 10 through a suspension line 8 at the upper portion of a rotor case 2. As a gyro section starts a precession with the rotation of the earth, the direction of a mirror 3 changes and a sensor 4 feeds an output equivalent to a declination α of a gyro rotor shaft from the sensor zero direction to a torque unit control circuit 5, which feeds an output -K(α+Td.dα/dt) to a torque unit. The torque unit applies a torque about a vertical shaft to the gyro section through a control plate 7. The gyro section separates by a certain angle with respect to the sensor zero direction and rests. The angle is connected to an azimuth θ of setting the body and the value θ is computed with a CPU9 from the output of a sensor 4 equivalent to the angle .