Patent ID: 7862461

Claim:
An automatic transmission, comprising one clutch that includes: a clutch drum; a piston that forms a hydraulic oil chamber using a part of the clutch drum as a cylinder; a plurality of friction plates that engage with the clutch drum; and a cancel oil chamber that is provided on a rear side of the piston and that cancels a centrifugal oil pressure that acts on the hydraulic oil chamber, wherein: oil is supplied to the cancel oil chamber from a boss portion formed in the clutch drum on a radially inner side, and the oil is discharged from discharge holes formed in the boss portion to an outside of a hydraulic oil chamber side of the clutch drum, a sleeve is fitted to an inner peripheral surface of the boss portion; recessed grooves are formed in an outer peripheral surface of the sleeve such that they are aligned with the discharge holes and extend up to an end face; and the oil from the cancel oil chamber is discharged via the discharge holes and the recessed grooves.