An automatic transmission that includes 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. 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.