In an external member, peripheral edge regions of first and second metal foil layers are joined via a periphery sealing portion containing thermoplastic resin. A plurality of bare cells are arranged separately in internal spaces surrounded by the first metal foil layer, the second metal foil layer and the periphery sealing portion. The partition region of the first metal foil layer between adjacent bare cells and the partition region of the second metal foil layer between adjacent bare cells are joined via the partition sealing portion. Thus, the internal space is partitioned into a plurality of independent individual spaces. At each individual space, the first metal foil inner exposed portion and the positive electrode portion are connected electrically, and the negative electrode portion of the second metal foil inner exposed portion and the bare cell are connected electrically. The bare cell and electrolyte are encapsulated in each individual space.