To attain a stop of driving in an input direction in an input side, influenced by the rotation of an output side, by self power, so as to obtain a smooth automatic continuously variable shift, in whatever rotational region of the output side in a planetary gear constitution.

With an input side ring gear 1 the planetary gears 2a, 2b, an output side sun gear 4 and a guide ring gear 3 are meshed, an output side sun gear 4a and a planetary gear 5a, a planetary gear 5b and a chassis fixed ring gear 6, and a planetary gear 5c and a guide ring gear 3, are meshed. In this way, turning force of the output side sun gear 4 drives the planetary gear which meshes with the chassis fixed ring gear 6 and the guide ring gear 3, driving in an input reverse direction of the guide ring gear 3 is performed, by the mutually meshed planetary gear 2, a driving stop in an input direction of the input side ring gear 1 is attained.