Cycloidal speed reducer

A cycloidal reducer includes a reduction unit configured to reduce a torque input and an output unit configured to transfer the reduced output to the outside. A cycloidal rotor that is one constituent element of the reduction unit has a tooth-type protrusion formed in the shape of a circular arc. Thus, the level of difficulty of process is decreased more than when the tooth-type protrusion in the related art is formed in the shape of a broken line. In addition, rotor pins are accommodated in through-holes, respectively, that are equally spaced in the cycloidal rotor. A bushing is formed that fills a gap between the through-hole and the rotor pin is formed in order for the rotor pin to stably transfer rotational power. Accordingly, the advantage of effectively distributing a load and stably transferring a reduction torque to the outside is provided.