PURPOSE: To enable engagement and idle running by engaging a member with a first cam mechanism by a correponding force with torque at the one way rotation time of a pair of members and engaging the member with a second can mechanism by the corresponding force with a generation thrust and pushing force at the opposite direction rotation time and giving an energizing force for separating the member to the second cam mechanism.

CONSTITUTION: The clearance between a first cam member 2 and a position 3 is increased by the normal rotation of a clutch disc 8 and the piston 3 and a second cam member 4 are pushed to the disc 8 and the member 4 is rotated normally and the cam surface of the member 4 raises the cam surface of the piston 3 through a second cam roller 6. The piston 3 is pushed back by the generation of cam thrust and the clearance between the member 2 and the piston 3 becomes minimum and the member 2 receives the reaction force of the cam thrust and the member 4 and the disc 8 are engaged by self binding. Thereby, the larger rotation torque, the larger engaging force. When the disc 8 is reversely turned, the member 4 is also reversely turned by friction engagement and the member 4 is engaged with the disc 8 by the cam thrust and this engagement force is the sum of the cam thrust and an oil pressure. When oil pressure thrust is reduced by the energizing force of a spring 7, the engagement is released.