PURPOSE: To make a device applicable to high loading and also make it extremely small is size by disposing a sun gear at the center of revolution, providing more than three epicyclic idle gears while being brought into contact with the sun gear, connecting a double side working flexible ring, the inner working circumferential length of which is shorter than the envelope circle of the working circle of each epicyclic idle gear, to each epicyclic idle gear, and thereby constituting an inner working outer ring to be connected to the flexible ring being ranged.

CONSTITUTION: A sun gear 1 is disposed at the center of revolution, more than three epicyclic idle gears 2 are disposed around the sun gear so that the epicyclic idle gears are set in epicyclic motion by means of the rotation of the sun gear 1. The inner teeth of a double side toothed flexible ring 3a the inner pitch circumferential length of which is shorter than the envelope circle of the pitch circle of each epicyclic idle gear 2, is arranged while being meshed with each epicyclic idle gear 2. An inner teeth outer ring 4 is arranged in the direction of each epicyclic idle gear 2 in such a way as to be meshed with the outer teeth of the double side toothed flexible ring 3.