A multi-disc frictional engagement mechanism includes a plurality of driven plates and drive plates, a hydraulic piston, a spring which comes into contact with a pressure receiving portion of the hydraulic piston, an oil chamber which causes a hydraulic pressure to act on the pressure receiving portion, and a lock mechanism which restricts a movement of the hydraulic piston in a coupling direction toward the driven plates and the drive plates in a state where the hydraulic pressure is supplied to the oil chamber, the spring is compressed by the pressure receiving portion and the driven plates and the drive plates are not coupled.