This cell comprises an electrode unit, a cell case in which the electrode unit is housed, and an insulated outer covering located between the electrode unit and the cell case. The electrode unit is housed, from an opening formed at an upper end of the cell case, in the cell case in a lateral direction in which a positive electrode collection component and a negative electrode collection component are disposed along from the upper end to the bottom at both ends of a wide face of the cell case, and is disposed inside the outer covering, to constitute an electrode insertion unit along with the outer covering. Here, the thickness (Lla) of the electrode insertion unit at both ends in the lateral direction steadily decreases from the upper end toward the bottom of the cell case.