Multi-stage reduction gear

A multi-stage reducer comprising a plurality of reduction parts each comprising an input shaft to which a rotation from a drive source is input, a cam provided on the input shaft, an external gear which is supported by an outer periphery of the cam and which revolves around a rotation center of the input shaft, a carrier which is coupled with the external gear and which is linked with a rotation movement of the external gear, and an internal gear which is meshed with the external gear and which rotates around the rotation center of the input shaft, the multi-stage reducer being configured to reduce the rotation from the drive source at a predetermined reduction ratio based on a difference between a number of gear teeth of the external gear and a number of gear teeth of the internal gear and to output the rotation having undergone speed reduction from either one of the internal gear and the carrier, wherein

• the plurality of reduction parts includes:
• a first-stage reduction part to which the rotation from the drive source is input;
• and
• a second-stage reduction part to which the rotation having undergone speed reduction by the first-stage reduction part is input, and
• the second-stage reduction part is disposed on an outer circumference of the first-stage reduction part.