PURPOSE: To control the reduction gear ratio at a low cost, by providing through cutting a slit, which is inclined to the axial line, on the outer peripheral surface of an outer ring, which is formed into a tapered surface, and fitting by pressure a control ring, whose inner surface is formed into a tapered surface, to the outer surface of the outer ring, thereby changing the diameter of the outer ring.

CONSTITUTION: When an input shaft 7 rotates, a rolling roller 18, which is connected to the input shaft 7 via an eccentric ring 14, rolls along the inner surface of the outer ring 19. As a result, the rotation of the rolling roller 18 is transmitted to an output shaft 8 via a flexible coupling 26. The outer peripheral surface of the outer ring 19 is formed into a tapered surface, and a slit that is inclined to the axial line is formed through cutting on a part of the peripheral surface. A control ring 20, whose inner surface is formed into a tapered surface, is fitted to the outer, tapered surface of the outer ring 19 by an appropriate amount, thereby shrinking the inner diameter of the outer ring 19. A leaf spring 16 is put into an eccentric gap between an eccentric ring 14 of the rolling roller 18 and the input shaft 7 and is kept at a position eccentric with the input shaft 7. Accordingly, the revolving speed of the rolling roller 18 changes in correspondence to the degree of shrinkage in the inner diameter of the outer ring 19, thereby enabling the control over the reduction gear ratio.