Abstract: An actuator for engagement and disengagement operation of a power transmission device is provided with a first plate being fixed, a second plate being movable in a direction of the engagement and disengagement operation so as to be engaged with the first plate, a third plate disposed opposite to the second plate with respect to the first plate, the third plate being rotatably engaged with the second plate, a drive unit engageable with the third plate so as to rotate the third plate, a cam mechanism converting a rotation of the third plate to a movement of the second plate in the direction of the engagement and disengagement operation and a retaining device restricting a relative rotation range of the third plate with respect to the drive unit. The second plate moved by the cam mechanism drives the power transmission device in the direction of the engagement and disengagement operation so as to intermit a power transmission thereof.

Abstract: An outer rotational member has an inner wall surface and an outer wall surface. An inner rotational member is arranged inside the outer rotational member. Friction-clutch means is provided between the inner rotational member and the outer rotational member and is fastened by a thrust force. An oil lubricates at least the friction-clutch means. An oil space intervenes between the inner rotational member and the outer rotational member. Seal means seals the oil in the oil space. A first oil reservoir is recessed on the inner wall surface of the outer rotational member toward a side of the outer wall surface side.