An automatic transmission including a first clutch, a second clutch, a first drum in which a first piston of the first clutch is axially slidably received and that cooperates with the first piston to define a first oil chamber, a second drum disposed coaxially with the first drum, so as to accommodate the first drum, and in which a second piston of the second clutch is axially slidably received, the second drum cooperating with the second piston to define a second oil chamber, a first fluid supply portion for feeding a working fluid into the first oil chamber through the first drum and the second drum, to operate the first piston, and a second fluid supply portion for feeding the working fluid into the second oil chamber through the second drum, to operate the second piston, and wherein the second fluid supply portion is located radially outwardly of the first fluid supply portion.