Sealing strips (20 and 21) are formed on an outer container (12) of an electric storage device (10) by heat sealing processing so as to surround an electrode housing portion (23). Further, a safety valve portion (21a) having a narrower sealing width than other sites is formed in the center of the sealing strip (21). Furthermore, a sealing strip (22) is formed on the outer container (12) to oppose the safety valve portion (21a) at a predetermined distance. When an internal pressure of the electrode housing portion (23) exceeds a prescribed value due to overcharge, etc., a sealing surface of the safety valve portion (21a) peels away, thereby opening the safety valve portion (21a) such that gas (G) in the electrode housing portion is discharged from the opened safety valve portion (21a). Electrode material and an electrolyte (X) are also discharged, but trapped by the sealing strip (22).