To construct a clutch mechanism which can perform an engaging operation at a given time and maintains engaging state reliably after the engaging operation.

The clutch mechanism includes: a weight member 12 freely movable in the radial direction relative to a support disk 11 provided to a shaft 3; and a portion 13 to be in contact on an inner circumferential surface of a driving pulley 7 in the outer position of the weight member. The clutch mechanism includes: a suppression spring 14 which biases the weight member 12 in a direction of a rotational axis X; an operating member 21 which is operative to a permitting position S for abutting against the weight member 12 and to a suppression position R for spacing from the weight member 12; and an actuator A which holds the operating member 21 to the suppression position R by the action of a negative pressure and operates the operating member 21 to the permitting position by releasing the negative pressure.