To provide a revolving section structure for a robot etc., which is simple and low in cost.

According to the revolving section structure, a driving rotating force of a driving motor 50 is directly transmitted from an external gear 52 fixed to an output shaft 51 to an external gear 53 fixed to a specific crank pin 37a, and thus the crank pin 37a of an eccentric differential reduction gear 17 is rotated. Therefore, compared with the case where the crank pin is rotated by transmission of the rotating driving force of the motor via a cylinder body having external gears on both ends thereof, the external gear on the cylinder body in mesh with the external gear of the motor can be omitted, and therefore the revolving section structure is simplified and the cost of the same is reduced.