PURPOSE: To achieve the extremely efficient transmission and speed change (continuously variable transmission) of the rotational motion.

CONSTITUTION: A rotary body 1 having a spherical surface and two other rotary bodies 3-1, 3-2 are provide. The spherical surface of the rotary body 1 having the spherical surface is held by two rotary bodies 3-1, 3-2 in a rotation transmitting manner. The relative position between the axis 11 of rotation of the rotary body 1 having the spherical surface and the axes 31-1,31-2 of rotation of two rotary bodies 3-1, 3-2 is changed by oscillating the axis 11 of rotation of the rotary body 1 having the spherical surface or turning it around the rotary body 1, and the rotation ratio between the rotary body 1 having the spherical surface and two rotary bodies 3-1, 3-2 is changed.