To highly accurately detect an azimuth of an own apparatus in an independent free space by utilizing a magnetic sensor with geomagnetism or a static magnetic field of artificial conditions as reference of the azimuth.

A first magnetic sensor 10, a second magnetic sensor 11 and a third magnetic sensor 12 wherein an output to an azimuth angle (θ) is V cos θ are combined so that they are orthogonal to one another, and a direction of a reference static magnetic field 4 is determined with an azimuth where azimuth angles (θ, ) are zero as reference. A unit azimuth vector and its three- dimensional inclination are known from an output vector 'V' including a first signal Dx output from the first magnetic sensor 10, a second signal Dy output from the second magnetic sensor 11 and a third signal Dz output from the third magnetic sensor 12 when a three-dimensional azimuth sensor is inclined with respect to the reference static magnetic field.