To provide a clutchless compressor capable of surely cutting off the transmission of rotational motive power to a rotary shaft of the compressor from a pulley at preset overload time without making the hub side heavy and large.

In a clutchless compressor having a hub 20 integrally arranged on a driving shaft 2 and a damper holding plate 50 for holding an elastic body for transmitting torque, when an overload is applied to an engaging mechanism 70 composed of a hole 56 formed in the damper holding plate 50 and a projecting part 25 formed in the hub 20, the damper holding plate 50 rotates against engaging force of the projecting part 25 and the hole 56, engagement of the projecting part 25 and the hole 56 is released, and the damper holding plate 50 runs on the projecting part 25 while pushing up a disc spring 60. When the damper holding plate 50 rotates by a prescribed quantity or more, a projecting part formed in the hole 56 and a pin 41 engage with each other, and the pin 41 rotates in the direction for loosening a nut 40 to reduce pressing force 60 of the disc spring 60 for energizing the damper holding plate 50 to idly rotate a pulley 10.