To sufficiently supply traction oil and sufficiently make it stay at a contact part between a low speed side ring and each roller so as to significantly improve the life.

On a side face of a second housing 2, a tip section 60 of the low speed side ring 32 is stored via a predetermined fine clearance, and a circumferential groove 61 extending in the circumferential direction is formed. In the circumferential groove 61, the outside diameter portion 62 and the inside diameter portion 63 are set almost at the same position in the axial direction. Traction oil existing in the inside diameter side portion of the low speed side ring 32 becomes a main stream to flow to the other (rightward direction : low speed shaft 3 direction) of the axial direction along the inside diameter portion of the low speed side ring 32, and flows in this direction in quantity, while a great deal of traction oil can be stored (can be stayed) in the inside diameter portion of the low speed side ring 32.