PURPOSE: To improve the workability and the stability at seamed part when top and bottom plates are seamed to a body of can.

CONSTITUTION: The body of drum can is formed by rounding a steel plate in a cylindrical shape and welding both edge parts superposed with each other. Both end parts of superposed part are pressed to be expanded utilizing welding residual heat by an upper die 69 and a lifted lower die 68 and a thickness equal to the thickness of one steel plate is obtained. Then, a blade 76 is lowered along back faces of dies 68 and 69 while the lower die 68 is still lifted. Thus, a swell-out part caused by rolling of superposed part is cut. Accordingly, the body having specific cylindrical shape and whose thickness of both end parts is uniform over all the circumference is obtained. Thus, the body and top and bottom plates are surely seamed.