To provide a non-interactive joint which is small, has a wide movable range, and in which one operation amount does not affect other operation amount.

A joint is formed by meshing a pair of spur gears 1a, 1b and a pair of spur gears 2a, 2b which differentially rotate coaxially through a gear for reversing. One of the pairs revolves around the other pair of the spur gears to change an angle of the joint. Thereby, even when the angle of the joint is changed, rotation of the gears is not affected, and the joint, which is not affected by the angle of the joint even when the gear is rotated, can be provided.