A power transmission device (10) comprises a rotatable rotary part (1, 2) to which a rotational drive force is transmitted from a drive source and a power transmission shut-off member (3) that shuts off transmission of an excessive torque between the rotary part and a rotating shaft (4) of a device to be driven. The power transmission shut-off member is threadedly coupled to the rotating shaft and can rotate with the rotating shaft. The rotary part is installed so as to be sandwiched between the power transmission shut-off member and the rotating shaft. A disc spring (8), installed between the power transmission shut-off member and the rotary part, is further provided. A caulked part (204a) for preventing a part of the power transmission shut-off member from dropping is provided on the front end side of the rotating shaft.