The present disclosure relates to a reducer. The reducer includes a casing, an internal ring gear and an elastic cushion. The casing has an inner circumferential wall provided with a first limiting part. The internal ring gear is arranged in the casing and has an outer circumferential wall provided with a second limiting part. The first limiting part is fitted with the second limiting part to limit rotation of the internal ring gear. The elastic cushion has at least a portion located between the second limiting part and the inner circumferential wall of the casing and abutting against the second limiting part and the inner circumferential wall of the casing.