To provide a power transmission mechanism to simplify structure and reduce a cost without employing an overload breakable material and besides, provide reliability on shut-off of power transmission.

In a power transmission mechanism, arms 2 and stoppers 6 are mounted on holes 1A for inserting a rivet formed in three spots of a pulley 1 by rivets 7. The arm 2 is rotatable around the rivet 7, the bending insertion part 6A of the stopper 6 made of a spring material is securely inserted in the hole 1B for inserting a stopper of the pulley 1, a bending lock part 6B can lock the arm 2. An elastic body 5 in the peripheral edge of which recessed engaging parts 5A are formed in the spots is fixed as a hub 4 by three rivets 8. When the pulley 1 is rotated clockwise, one end 2C of the protrusion-form engaging part of the arm 2 presses one end 5B of the recessed engaging part of the elastic body 5, whereby bending occurs to the elastic body 5. When a rotation force exceeds a set value, the arm 2 is rotated clockwise around the rive 7 and separated away from the recessed engaging part 5A of the elastic body 5.