Abstract: A substantially U-shaped sealing strip and a sealing strip are formed on an outer container of the electric storage device as first sealing strips by heat sealing processing so as to surround an electrode housing portion. Further, a safety valve portion having a narrower sealing width than other sites is formed in the center of the substantially U-shaped sealing strip. Furthermore, a second sealing strip is formed on the outer container to oppose the safety valve portion at a predetermined distance. When an internal pressure of the electrode housing portion exceeds a prescribed value due to overcharge, etc., a sealing surface of the safety valve portion peels away, thereby opening the safety valve portion such that gas in the electrode housing portion is discharged from the opened safety valve portion. Electrode material and an electrolyte are also discharged, but trapped by the second sealing strip.