Automatic transmission

An automatic transmission, comprising:

• a brake including a hub member coupled to a transmission case;
• a drum member coupled to a given rotary member;
• a plurality of friction plates disposed between the hub member and the drum member;
• and
• a piston configured to engage the plurality of friction plates, and a hydraulic chamber for engagement disposed radially inward of the hub member and to which hydraulic fluid for biasing the piston in an engaging direction;
• wherein the piston includes a pressing part configured to press the friction plates, a hydraulic chamber for engagement forming part forming the hydraulic chamber for engagement, and a coupling part coupling the pressing part to the hydraulic chamber for engagement and extending radially,
• wherein the hub member includes a plurality of spline parts with which the friction plates are spline-engaged in circumferential directions,
• wherein a plurality of notches formed by cutting the coupling part of the piston so as to be spaced apart from each other in the circumferential directions, and
• wherein end parts of the spline parts of the hub member in axial directions enter into the notches of the piston.