PURPOSE: To enable the holding of the pressure welding force and the transmitting force capacity with proper value neither more nor less, by setting the transmitting force capacity magnification as a magnification to the given transmitting force and enabling the friction transmission when the eccentric quantity of a transmission ring is set.

CONSTITUTION: The elastic deformation of a rigid body ring 11 by the transmit ting force is controlled by the rigidity of the rigid body ring 11 of the transmis sion ring 1, and at the contacted part of the V-shape channel parts b, b of the main and the slave pulleys 2, 3 with the V-shape projecting part a of the elastic body ring 12, the elastic body ring 12 itself is elastically deformed by the pressure welding force of the same part so that the contacted area is secured enlarging without the deformation of the channel parts b, b of the opposite side. When the eccentric quantity δ of the ring 12 or the angle corresponding to it is properly set, the work to hold the certain transmitting force capacity magnification equal to the one in the case when the material of the contacted part is hardened steel and the condition of the contacted face needs the lube oil, is obtained.