PURPOSE: To prevent the degradation caused by power loss of the performance of a fastening device and to improve its durability by providing a passage extending axially in an engaging part between the protrusion part of the first transmitting member and the recess part of the first plate.

CONSTITUTION: The protrusion part 2a of a clutch drum 2 as the first transmitting member is provided with a groove 12 as a passage extending axially, and the section of the groove 12 is about U-shaped. A wet multiple plate clutch is engaged or disengaged with the movement of a piston 6. In this case, when centrifugal force caused by the rotation of a driving plate 3 or a driven plate 1 makes radiating fluid move into an engaging part between the recess part 1b of the driven plate 1 and the protrusion part 2a of the clutch drum 2, the radiating fluid can flow through the groove 12 provided on the protrusion part 2a to reduce its stay in the engaging part.