A rectangular charging device is provided with: a group of rectangular columnar electrodes including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and having a top surface, a bottom surface, and four side surfaces; an electrolyte; a case that has an opening and accommodates the group of electrodes and the electrolyte; a sealing plate that seals the opening of the case; and an insulating sheet that is interposed between the group of electrodes and the case so as to insulate the group of electrodes from the case. The insulating sheet is folded so as to cover the bottom surface and the four side surfaces of the group of electrodes.