PURPOSE: To provide a vibration reducing device which is simple in structure and does not enlarge load.

CONSTITUTION: An elliptical guide rail 2 is attached to a crankshaft 1, and a balance weight 3 is reciprocatably supported by a support part 4 formed in an engine body. A pair of shafts 5 is fixed to the balance weight 3, and a roller 6 is severally rotatably attached to the shafts 5, and rotates on the guide rail 2. The balance weight 3 reciprocates twice for one rotation of the crankshaft 1 to generate inertia force to deny the excitation force of the secondary vibration of the engine. The above inertia force can correspond to the vibration composed of the excitation forces having different order by altering the shape of the guide rail.