PURPOSE: To increase the wedging operation of a conical rotor by making the transmission surface of the conical rotor to which a large diameter transmission element is friction-contanted in a concaved conical surface, and keeping the vertical angle of a conical surface to friction-contact to the inner surface of a speed change ring, the vertical angle of the concaved conical surface, and the difference between the both vertical angles in a specific relation.

CONSTITUTION: While a conical rotor 10 has a conical surface 12 to friction- contact to the inner surface of a speed change ring 11, it is friction-contacted to a large diameter transmission element 13 and to a small diameter transmission element 14. That is, the conical rotor 10 is held at three points, the speed change ring 11, the large diameter transmission element 13, and the small diameter transmission element 14. When the vertical angle of the conical surface 12 is made θ, and the vertical angle of a concaved conical surface 15 of the conical rotor 10 is made , a condition is given to them as 150≥θ≥130°, 170°≥≥150°, and 40°≥-θ≥20°. By satisfying this condition, the wedging operation by the conical rotor 10 is made stronger while keeping a thrust applied to the conical rotor 10 small, and the transmission efficiency is improved.