A pressing member 44 is pressed from the outside against a peripheral wall of a can shell 4 whose interior is maintained at a predetermined pressure by gas, to form a recess-deformed portion 56 having a predetermined shape on the peripheral wall of the can shell 4. Thereby, three-dimensional patterns can be formed by recess-deforming desired portions of the can shell 4 while preventing the strength of the can shell 4 from being deteriorated and preventing the inner surface of the can shell 4 from being scratched or the coating from being damaged, by which outer shape processing with high design performance can be easily applied to the can shell 4 at a low cost.