Method for manufacturing a device case body and method for manufacturing a power storage device

A method for manufacturing a device case body, which is made of metal in a tubular shape and used for a power storage device, the method comprising:

• inserting an insertion unit of a cutting assist device into a metal tubular member having a hollow tubular shape extending in an axial direction along an axis of the metal tubular member, through a leading-end opening that opens on a leading end side of the metal tubular member, beyond a to-be-cut portion of the metal tubular member, the to-be-cut portion extending in a ring shape in a circumferential direction around the axis;
• cutting the to-be-cut portion by irradiating a laser beam from outside in a radial direction of the metal tubular member onto the to-be-cut portion to obtain the device case body;
• and
• removing the insertion unit from the metal tubular member after the device case body is cut by cutting the to-be-cut portion,
• wherein the insertion unit includes a facing recess that is recessed to an inside of the insertion unit in the radial direction and that includes a facing opening extending in a ring shape and facing the to-be-cut portion of the metal tubular member, and
• in cutting the to-be-cut portion, the metal tubular member is cut while a penetrating laser beam that penetrates through the metal tubular member is received by the facing recess.