To easily disengage and reengage a clutch by arranging at least one means to move a torque transmitting member between an actuating position and an non-actuated position independently of a joining means.

When the transmission of maximum torque is required, a reaction member 7 is rotated in the direction of a second driving member by a hexagonal structure 28, and a disc spring washer 39 of a main energizing means is compressed to the maximum extent. A projecting part 54 of a torque transmitting means 21 is received in a torque transmitting recessed part 52, and torque is transmitted between a first and the second driving members. When the torque exceeds a prescribed value, a corresponding surface of the projecting part 54 and a recessed part 52 imparts reaction to the member 21, and the member 21 is energized in the rightward direction by a ball element 43 by the wedge action of a surface 42 of a constitutive part 40, and the part 40 is energized in the leftward direction by the reaction of the washer 39. As a result, the ball element 43 moves outward in the radial direction, and the member 21 moves to a non-actuated position in the rightward directional. However, it is automatically returned to an actuating position by an auxiliary energizing means by the disc spring washer 32.