PURPOSE: To reduce the noise in the vicinity of a pulley mechanism fitting part by forming a plurality of ribs projecting in a void on the inner circumferential surface facing the void, and fixing the noise absorbing material at least between the ribs in the void in a pulley mechanism provided with a pulley body where an open void is formed on the inner circumference on the shall end side.

CONSTITUTION: A rubber 3 is interposed between the inner circumference of a pulley 1 to which a V belt for driving an auxiliary machine is stretched and the outer circumference of a hub 2, and a plurality of semi-columnar ribs 11 are projectingly provided on an inner circumferential surface 2b opposite to a conical void 2a of the hub 2 at an equal interval in the circumferential direction facing the void 2a. Each rib 11 is formed so that the distance between the adjacent ribs 11 may be larger on the outer circumferential side than on the inner circumferential side to prevent the fall-out of the noise absorbing material 12 to the inner side. The noise absorbing material 12 consisting of foaming rubber made of two-liquid type silicone rubber is mounted in the conical void 2a of the hub 2, and its outer circumference is adhered to the inner circumferential surface 2b facing the void 2a of the hub 2.