A window portion allowing the terminal of the cell to be inserted through is opened in the board holder, and projecting portions are provided projecting inward in the window portion in plural locations of the edge sides facing the window portion in the board holder. And the plural projecting portions in the board holder each decrease in cross-sectional size toward the tips of the plural projecting portions, the board holder is engaged in position by the tips of the plural projecting portions at least partially contacting the under surface of the terminal of the cell which is exposed to the sealing plate side without being covered by a gasket.