PURPOSE: To eliminate the necessity of a gear train so as to reduce manufacturing costs by moving a link on its trajectory surface by the rotation of an input shaft, rotating an output shaft by the trajectory motion of the link and connecting one shaft to the link by a pin extending in parallel with an axis.

CONSTITUTION: A link 12 is driven on a trajectory by the rotation of a crankshaft 10, and pins 20 and 21 are moved on a circular path. The pins 20 and 21 are respectively moved up and down in grooves 25 and 26, and a camshaft 11 rotated by half for each full rotation of the crankshaft 10. When any one of the pins 20 and 21 is positioned in the center of the groove 25 or 26, the motion direction of the pin becomes parallel to the groove to make torque transmission zero, but the other pin is moved vertically to the groove 25 or 26, and torque transmission becomes maximum. Thus, by the combination of respective reactive forces between the pins 20 and 21 and the grooves 25 and 26, over the full rotation of the crankshaft 10, torque is uniformly transmitted from the link 12 to the cam 11, and a torque transmission mechanism needing no gear trains is provided.