Angle-adjusting device

Angle-adjusting device (1) includes an internal gear (11, 12) including at least an inner gear (8) and an outer gear (7). The internal gear is connected to either a fixed arm (9) or a movable arm (10). The angle-adjusting device further includes an external gear, which has a central axis (20) eccentric relative to a central axis (21) of the internal gear, and includes at least the inner gear and the outer gear. The external gear is connected to either the movable arm or the fixed arm. A pitch circle for the inner gear is common to a pitch circle for the outer gear, a number of teeth on the external gear is less than a number of teeth on the internal gear, the central axis for the external gear revolves around the central axis for the internal gear, and backlash of the inner gear is different from backlash of the outer gear.