PURPOSE: To construct a variable angular velocity ratio transmitting mechanism for rotating a crankshaft of an internal combustion engine at non-equal velocity without using any non-circular gears while roughly holding the rotation of an output shaft at a constant, and prevent pulsation of output torque at low and high speeds of the engine.

CONSTITUTION: A rotation of an input shaft 13a is transmitted from a gear 9a to a gear 9d of an output shaft 14 through gears 9b and 9c supported with an inner housing 10 by ordinary circular gears 9a to 9e of a variable velocity ratio transmitting mechanism 8 connected to a crankshaft 2 of an engine 1. Also the inner housing 10 is oscillated around the output shaft 14 by a rod 22 provided on a crank part 21a of a shaft 21 through the gear 9e and sliders 23a and 23b provided on the inner housing 10. By this, the gears 9b and 9c are oscillated together with the inner housing 10 in mesh with the gears 9a and 9d, respectively. Thus, if the rotation of the output shaft 14 is kept constant by a flywheel 15, the input shaft 13a (crankshaft 2) makes a periodic non-equal velocity motion.