Method for producing pouch battery

A method for producing a pouch battery, the method comprising

• inserting a cell stack in a laminate film exterior body,
• sealing the outer perimeter edges of the laminate film exterior body in which the cell stack has been inserted, in an airtight chamber in a state of reduced pressure,
• applying tensile force outward in the in-plane direction at two facing locations in the in-plane direction on the outer perimeter edges of the laminate film exterior body by using holding devices that hold the two facing locations in the in-plane direction on, the outer perimeter edges of the laminate film exterior body, thereby forming spaces between the laminate film exterior body and both ends of the cell stack in the in-plane direction, and
• raising the pressure in the airtight chamber to atmospheric pressure, so that the spaces contract, while maintaining the application of tensile force outward in the in-plane direction of the laminate film exterior body, wherein during the raising the pressure, the holding devices move inward in the in-plane direction due to contraction of the spaces caused by the raising the pressure in the airtight chamber.