Abstract: The invention provides a wave speed reducer having a self-locking function comprising a structure for outputting driving rotation of a bearing member or a spline wheel at a specific reduction ratio which drives rollers to rotate by a cam. A designed convex arc of the cam has self-locking function of restricting the rollers to reversely rotate so as to form a compound type reducer device having a multi-reducer function by mutually combining the wave speed reducer and a planetary gear set. To solve conventional problems, poor driving accuracy at tiny rotation angle and scarcity of self-locking function for conventional reducers are improved.