Cell tube and method of manufacturing the cell tube

A manufacturing method of a battery case, comprising:

• a first step of manufacturing a battery case element (7) by applying drawing processing and ironing processing by pushing a cup-shaped intermediate product (4) by an external punch (20) to pass through a drawing die (10) and ironing dies (11, 12, and 13) aligned in multiple stages, all of which are aligned in series, so that a thickness (t1) of a side wall (7a) with respect to a thickness (t0) of a bottom wall (7b) satisfies t1=αt0 (α=0.2 to 0.7);
• stopping said external punch when a tip end portion thereof has passed through the ironing die (13) at a last stage in said first step, whereupon an internal punch (21), which is allowed to go into and come out from said external punch, projects from said external punch and continues to move ahead;
• and
• a second step of manufacturing a battery case (1) by reducing an outside diameter to a predetermined diameter without changing the thickness of the side wall, by applying drawing processing by pushing said battery case element by said internal punch to pass through a plurality of drawing dies (18 and 19) aligned in series contiguously to a latter stage side of said dies in said first step.