PURPOSE: To eliminate angle transmission loss at low noise by connecting to each other a plurality of steel balls annularly arranged among a fixed sun disc, a driving sun disc and a driven sun disc by means of a cylindrical separator and rotatably holding them by means of both non-magnetic bodies capable of rotating around the center axis of the driving sun disc.

CONSTITUTION: When a driving sun disc 2 is rotated by a driving shaft 6, a plurality of steel balls 4a, 4b on the both sides are rotated. In this case, the steel balls 4a, 4b are held by respective ring plates 8a, 8b, and both ring plates 8a, 8b are connected to each other by a separator 11, moreover, the steel balls 4a, 4b are fitted into a ring groove 10 of the fixed sun disc 1 or the driven sun disc 3, so that the steel ball on the one side and that on the other side revolve in the same direction at the same speed while being rotated at the different rotation speed. Therefore, the driven sun disc 3 is so deccelerated as to reduce and rotate the driven shaft 9 connected thereto. Moreover, the ring plate is rotatably held by a bearing, so that noise can be prevented.