To complement shortage of a moving force given to the first end of a torsion spring in such a situation that the movement of the first end stagnates solely with the energizing force of a released energizing means when the first end is released by a releasing means from the restriction surface.
A get-on part 51 is formed on a rotor 41. In the situation that the outer end 47a of a spiral spring 47 is hitched by the inner peripheral surface of the rotor 41 to cause stagnation of the movement in the axial L direction at the time of excessive load torque releasing, the spiral spring 47 gets on the get-on part 51 with the relative rotation of the rotor 41 with a rotary shaft 16. Accordingly a moving force directed ahead in the axial L direction is given to the outer end 47a so as to complement shortage of the moving force solely with the energizing force of the spiral spring 47, and the outer end 47a is moved ahead in the axial L direction.
TANAKA HIROHIKO
URYU AKIHITO
OKADA MASAHIKO
