A friction engagement device equipped with a forward clutch (5) and a clutch operation pack (6) that controls the fastening/releasing of the forward clutch (5), wherein the clutch operation pack (6) has: a hydraulic piston (61); a fastening pressure piston chamber (62); a snap ring (64); diaphragm springs (65); and a ball-lock mechanism (BL). The diaphragm springs (65) impart biasing fastening force to the forward clutch (5) on the clutch side of the hydraulic piston (61). The ball-lock mechanism (BL) restricts the movement of the hydraulic piston (61) in the release direction at the position where the forward clutch (5) becomes fastened by the biasing fastening force when on-pressure acts upon the fastening pressure piston chamber (62), and after the movement of the hydraulic piston (61) is restricted, the ball-lock mechanism continues to restrict the movement of the hydraulic piston (61) in the release direction, even after the on-pressure in the fastening pressure piston chamber (62) is removed.