Cylinder for automatic transmission

In a structure for an automatic transmission wherein a brake (110) is arranged in a casing, a hydraulic servomechanism for actuating the brake includes a cylinder (161), a piston (162), a return spring for biasing the piston and including an annular portion (164a) abutting on the piston and a plurality of leaf-spring portions (164b) protruding outward equiangularly from the outer periphery of the annular portion, and a plurality of pressing portions (163) formed with the piston and abutting on the servomechanism through clearances between the leaf-spring portions of the return spring.