PURPOSE: To accurately measure the rotation of the magnetic field of the earth by providing a two-axial rate gyroscope for measuring the angular velocity of a vehicle, a suspension type magnetometer medium for measuring the magnetic field of the earth inside three orthogonal axes, a horizontal display unit, and a controller.

CONSTITUTION: The compass system 10 consists of the two-axial rate gyroscope 12 for measuring the angular velocity of the vehicle, the suspension type magnetometer medium 14 for measuring the magnetic field of the earth in the three orthogonal axes, the horizontal display unit 18, the controller 20 equipped with a mathematical central arithmetic unit which processes the output of an instrument and the input of operation to be performed and controls system operation, and a coupling device 22 for the operation to be performed which is equipped with a display for showing flight direction data on the vehicle and other system data and a medium for making a person who operates input instructions. Then the device 22 makes the person who operates input instructions for starting, controlling, and ending the system. Further, the person is made to receive data, based upon the instrument, which are generated by the system including a flight direction. Furthermore, the person is made to receive data based upon the state of available operation of the system.