PURPOSE: To accomplish low noise and low vibration by furnishing an elastic member having large friction coefficient and anti-abrasiveness on the friction surface of a planet roller or an eccentric element of an input shaft or a metal housing inner wall, increasing the linear contacting force, and by obtaining reduction gearing ratio with high precision.

CONSTITUTION: An elastic member 52 having a large friction coefficient and anti- abrasiveness is provided on the internal circumferential wall surface 14a of a metal housing body 12 in such an arrangement as capable of being in contact freely with No.1, No.2 eccentric element 26, 36 and elastic rings 34, 44. Through a pin 29, an elastic ring 34 having large friction coefficient and anti-abrasiveness is installed consolidatedly in threaded through holes 32b bored near the peripheral edge of an outer race 32 at a certain spacing to accomplish No.1 eccentric element 26 capable of being in contact freely with the circumferential inner wall 14a of the housing 10. Through the pin 29, also, another elastic ring 44 is provided consolidatedly in threaded through holes 42a bored near the peripheral edge of another outer race 42 at a certain spacing to achieve No.2 eccentric element 36 capable of being in contact freely with the inner wall surface 12a of the housing 10. Further, an elastic member 52a having large friction coefficient and anti-abrasiveness is furnished on the inner side face of another housing 62 or the sun roller 68.