PURPOSE: To suppress generation of noise by attaching a pulley cover which covers an outer face of a crank pulley to a projected face of a rim and providing a resonator room for silencing in the inside of a crank shaft.

CONSTITUTION: A crank pulley 10 which is attached to a crank shaft 21 of an engine has a boss 11, a rim 13 which attaches a belt on an outer periphery 131, and an arm 12 which connects the boss 11 and the rim 13. In this case, a projected face 132 which projects outwardly than the boss 11 and the arm 12 is formed on the opposite side of the crank shaft 21 on the rim 13, and a pulley cover 15 which covers an outer face of the crank pulley 10 is attached via a vibrationproof rubber as a buffer member 19 on the projected face 132. Also, a resonator room 23 for silencing is provided in the inside of the crank shaft 21, and the resonator room 23 is communicated with a space in pulley inner wall 18 via a communicating passage 17 to constitute a resonator which is useful in reducing noise by both of the communicating passage 17 and the resonator room 23.