A package case is structured by a plurality of substantially identical and flat frames stacked on one another. Flat laminate cells (accumulator cells) are individually accommodated in the frames and stacked on one another, so that the number of flat laminate cells (accumulator cells) can readily be changed simply by increasing/decreasing the number of frames to be stacked to meet energy needs and the like. The accumulator device is segmented using the plurality of flat frames, so that externally applied impacts can readily be dispersed and the impact transmitted to the flat laminate cells (accumulator cells) can be reduced without reinforcing the accumulator device 1 with more than necessary strength.