To improve the operation responsiveness by reducing the resistance of the operating fluid as much as possible when operating a piston plate with the electromagnetic force.

An input shaft 12 of a transmission is provided with a piston plate 17 freely to be moved forward and backward in the axial direction. This plate 17 is moved forward and backward by the magnetic force of a solenoid 28 and the controlled hydraulic pressure to be applied to a front and a rear operation chambers 19, 20, and when moving the plate 17 forward and backward, the plate 17 and a housing 13 are frictionally engaged with each other. The piston plate 13 is provided with a through hole 34, and provided with a check valve 37 for opening the through hole 34 when the pressure of a shutoff operation chamber 19 is larger than that of the connecting operation chamber 20. When connecting the clutch with the electromagnetic force, since the check valve 37 opens the through hole 34 so as to allow the flow of the hydraulic fluid between both the operation chambers 19, 20, resistance by the hydraulic fluid to be applied to the plate 17 is reduced.