A piston (26) for an automatic speed changer, the piston being made by pressing, and having a hollow-cylindrical section (28) and a bottom section (30) provided on one end side of the hollow-cylindrical section (28). A part of the hollow-cylindrical section (28) is cut and bent up radially outward to form a claw section (52) engaging with a projection section (56) provided on a case (12). Since the claw section (52) as a rotation prevention structure is formed by cutting and bending a part of the hollow-cylindrical section (28), the material size of the piston (26) is not necessary to be large to provide the claw section (52). As a result, despite the piston (26) having the rotation prevention structure, it can be produced at low cost. |