To cut down on cost by improving layout performance, and by improving productivity.

A disk-shaped gear 2 and a ring-shaped gear 3 are concentrically arranged so as to be adjacent to each other, a drum 8 which extends in the axis direction 6 from the axial core position of the one-side surface of the discoidal gear 2 toward a hollow part 4 of the ringlike gear 3 is protrusively arranged, a block plate 16 having an axial hole 15 which allows the penetration of the drum 8 so as to be capable of supporting it is attached to the other side surface of the ring-shaped gear 3, a shoe 18 which can contact with the drum 8 so as to be slidable from the inside surface of the block plate 16 of the ring-shaped gear 3 is protrusively arranged, and a press spring 23 which can make the shoe 18 press-contact with the drum 8 is interposed between the internal peripheral surface of the ring-shaped gear 3 and the shoe 18.