A coupling device has a pulley that receives rotational torque from an engine. The torque is transmitted to a shaft through a hub and a one-way clutch. A torque limiter is screwed on the shaft to fasten the inner ring of the one-way clutch onto the shaft. The torque limiter has a breakable portion. The torque is directly transmitted from the inner ring to the shaft when the torque is normal. If the torque exceeds the tightening torque of the torque limiter, the inner ring begins to slide and rotate, and drives the torque limiter in a tightening direction. As the torque limiter is tightened additionally, the tensile stress on the breakable portion is increased. Then, the breakable portion breaks and is separated in axial direction so that the coupling device disconnects torque transmission.