Speed reducer

A speed reducer comprising:

• an input unit including an input shaft and a first bearing, the first bearing including an eccentric first inner ring that rotates together with the input shaft and a first outer ring that is located radially outward of the first inner ring;
• a cycloid gear located radially outward of the first bearing and including a plurality of external teeth arranged on an outer peripheral surface along circumferential directions, the cycloid gear including a first through hole the input unit penetrates and a plurality of second through holes located radially outward of the first through hole and arranged with intervals in the circumferential directions;
• a plurality of inner pins penetrating the second through holes in axial directions;
• an inner pin holder holding end portions of the plurality of inner pins in the axial directions and surrounding an outer peripheral surface of the input unit;
• a second bearing located radially outward of the cycloid gear, and including a second inner ring that is an output shaft, a second outer ring located radially outward of the second inner ring, and a rolling body located between the second inner ring and the second outer ring;
• and
• a plurality of outer pins held on a radially inner surface of the second inner ring and meshing with the external teeth of the cycloid gear, wherein
• the second through holes are elongated along the circumferential direction,
• the first inner ring is provided separately from the input shaft, and
• the input unit includes a movement restrictor that restricts movement of the first inner ring relative to the input shaft in the circumferential directions.