Patent ID: 7666100

Claim:
A power transmission device comprising: a rotatable rotary part to which a rotational drive force is transmitted from a drive source; and a power transmission shut-off member that shuts off transmission of an excessive torque between the rotary part and a rotating shaft of a device to be driven, is coupled by threads to the rotating shaft, and is capable of rotating together with the rotating shaft as one body, wherein: the rotary part is installed so that one side of the rotary part comes into contact with the rotary shaft and another other side of the rotary part faces the power transmission shut-off member; the power transmission device further comprises an elastic member installed between the power transmission shut-off member and the rotary part; and the elastic member exerts a repulsive force on the power transmission shut-off member and the rotating shaft in a direction to separate the rotating shaft and the power transmission shut-off member.