Patent ID: 7862465

Claim:
An automatic transmission, comprising: two clutches that are provided in mutually different positions in a radial direction while overlapping each other in an axial direction, the two clutches each including: a clutch drum; a piston that structures an operating oil chamber while using a part of the clutch drum as a cylinder; a plurality of friction plates that engage the clutch drum; and a cancel oil chamber that is disposed on a back face side of the piston and that cancels a centrifugal hydraulic pressure acting on the operating oil chamber, wherein: the operating oil chamber and the cancel oil chamber of one clutch of the two clutches positioned on a radially outer side are respectively positioned on a radially outer side of the operating oil chamber and the cancel oil chamber of the other clutch of the two clutches positioned on a radially inner side, the clutch drum of the one clutch of the two clutches includes an inner circumference side member and an outer circumference side member that are integrally structured, the inner circumference side member including a boss portion and a piston supporting portion, and the outer circumference side member including a drum portion and a bottom portion, and an oil passage through which a hydraulic pressure is supplied and discharged to and from the operating oil chamber of the one clutch of the two clutches is formed between the inner circumference side member and the outer circumference side member.