Method for manufacturing film-packaged cell

A film-packaged cell has a flat rectangular shape where power-generating element is housed in packaging body together with an electrolytic solution, the film-packaged cell being sealed along four edges of the packaging body in a state where terminals are led out through one edge thereof. In an electrolyte injection step, the electrolytic solution is injected into bag-shaped body where three edges excluding the upper edge of the packaging body are sealed in an orientation where the terminals are protruding laterally, the electrolytic solution being injected from the side of the opening upper edge. In a partial sealing step performed before the electrolyte injection step, only one section of opening upper edge of the bag-shaped body near edge through which terminals are led out is partially sealed, thereby preventing the electrolytic solution from leaking out during electrolyte injection.