Reducer

A reducer includes a reduction unit configured to reduce an input torque, and an output unit configured to be supplied with a preset reduction torque through the reduction unit and to transfer an output torque to the outside. The reduction unit includes an input shaft configured to be supplied with the input torque, a cycloidal disc arranged on an outer circumferential surface of the input shaft in an eccentrically rotatable manner, a tooth-type protrusion being formed along a circumference of an edge of the cycloidal disc, a hollow housing configured to accommodate the cycloidal disc and including a plurality of inner pins arranged to be spaced a predetermined distance apart from each other along a circumference of an inner circumferential surface of the hollow housing in a manner that possibly comes into contact with the tooth-type protrusion on the cycloidal disc, and a plurality of rolling pins coupled to the cycloidal disc and having a cylindrical structure.