To shut off current flowing between electrode plates by low pressure, and enlarge the adjusting range of current shut off pressure in a square power storage element.
A positive electrode plate and a negative electrode plate 21a are stacked through a separator 21b, then they are wound in a non-complete round shape to form an electrode group 21, and the electrode group 21 and an outer can 22 for housing the electrode group 21, having the square cross section, and electrically connected to one electrode plate of the electrode group 21 are arranged to form a square power storage element 20. A contact piece 23 for electrically connecting one electrode plate to the side wall 22a of the outer can 22 is formed in one electrode plate to which the outer can is connected. By the deformation of the side wall of the outer can caused by increase in pressure within the outer can, the side wall of the outer can is separated from the contact piece.
TAMAI MASAHIRO
HARADA YOSHIRO
NAKANISHI MASANORI
