Automatic transmission

An automatic transmission comprising a clutch device, wherein

• the clutch device comprises:
• a clutch hub comprising an inner-side cylindrical portion located on a radial-direction inner side;
• a clutch drum comprising an outer-side cylindrical portion disposed on a radial-direction outer side of the inner-side cylindrical portion;
• a friction plate provided slidably between the inner-side cylindrical portion and the outer-side cylindrical portion;
• a piston which presses the friction plate from a first axial-direction side;
• and
• a hydraulic chamber to which operating oil which urges the piston in a direction of the friction plate is supplied,
• the clutch drum comprises:
• a disc-shaped first radial-direction portion extending from an end portion of the outer-side cylindrical portion on the first axial-direction side toward the radial-direction inner side;
• a comb-teeth shaped axial-direction portion extending from an end portion of the first radial-direction portion on the radial-direction inner side toward a second axial-direction side;
• and
• a disc-shaped second radial-direction portion extending from an end portion of the axial-direction portion on the second axial-direction side toward the radial-direction inner side,
• the piston comprises:
• a pressing portion disposed between the first radial-direction portion and the friction plate to press the friction plate;
• and
• a disc-shaped piston radial-direction portion extending toward the radial-direction inner side from the pressing portion,
• the hydraulic chamber is provided on the radial-direction inner side from the axial-direction portion of the clutch drum and on a non-friction-plate side of the piston radial-direction portion, and
• a comb-teeth portion is provided at a radial-direction intermediate portion of the piston radial-direction portion, and the axial-direction portion and the piston radial-direction portion intersect with each other in a comb-teeth shape.