A power transmission device of a compressor includes a rotary shaft, a pulley, a hub, a power shutoff member, a spacer and a cylinder. The power shutoff member shuts off excessive torque transmission between the pulley and the rotary shaft of the compressor. The spacer is disposed on the rotary shaft. The cylinder is disposed between the power shutoff member and the rotary shaft. The cylinder has an external thread portion formed at the outer periphery thereof for engagement with an internal thread portion of the power shutoff member and an internal thread portion formed at the inner periphery thereof for engagement with an external thread portion of the rotary shaft. The cylinder has a contacting surface for contact with a seating surface of the spacer and a seating surface for contact with a contacting surface of the hub at the axial end portion of the hub.