To provide a method and an apparatus for more efficiently manufacturing a cylinder device that has an opening edge of its base shell subjected to machining of rocking-curling and has less variation in the residual axial force to affect an inner tube.

A rocking-curling die 3 is moved in such a combined rocking motion that, while making a precessional rocking movement, the die 3 makes an in-plane rocking movement N times (N1) per one time of the precessional rocking movement. Thereby, drawing-in force (a metal flow) from the outside to the inside is generated at an opening edge 2a of a base shell 2, so that plastic flow makes the opening edge 2a to be drawn in from the outside to the inside. As a result, spring back of the opening edge 2a after machining of rocking-curling is restrained, and the residual axial force of an inner tube 30, which is obtained by the machining of rocking-curling, is secured. Thus, a cylinder device whose inner tube 30 has less variation in the residual axial force is more efficiently obtained.