To provide a detecting device lightweight with high sensitivity by measuring an eccentric turning angle of a rotator eccentrically rotatable by gravitational action, and detecting a gravity direction from the turning angle.

Capacitance between a rotator 11 and an electrode 12a measured by a capacitance measuring apparatus 12b at a reference point of a turning angle 0 of a disc 11a is made C0. When a gravity direction detecting device is installed at a certain inclined place, the disc 11a is drawn by a weight 11a and eccentrically rotated by θ1 from the reference point, so that a clearance D1 between the electrode 12a and the outer periphery of the disc 11a becomes larger than a clearance D0 at the reference point, and measured capacitance C1 becomes smaller than CO. The clearance D1 is obtained from the capacitance C1, the turning angle θ1 is obtained from the clearance D1, and a gravity direction (g) can be obtained from the turning angle θ1. When the capacitance C1 is reduced, it is so judged that the disc 11a is rotated counterclockwise, from which the inclined direction of the inclined place can be detected.