To improve responsiveness by reducing spherical weight, to facilitate the balance adjustment, and to miniaturize the whole device, in an azimuth detector employing a floating sphere.

A plurality of optical sensors 11a, 11b and 11c are arranged at an interval on the inner surface of a light shielding case 9 formed so that the inner surface becomes a spherical surface, and a shape member 3 that is a sphere with a diameter smaller than the diameter of the case 9 and has a built-in permanent magnet 7 is stored in the inner surface of the case 9. Transparent liquid is filled between the inner surface of the case 9 and the shape member 3 to float the shape member 3 freely, and the permanent magnet 7 is arranged on a specific diameter of the shape member 3, at a position separated from the center, and symmetrically with respect to this diameter, so that the shape member 3 becomes stable in a floated state while the permanent magnet 7 lies on the downside. The surface of the shape member 3 is made to have color of a contrast region where the degree of the contrast varies gradually and continuously in the rotation direction about the diameter as the rotation symmetry axis, and the azimuth is determined and displayed based on output signals of the optical sensors for detecting this contrast region.