In a secondary battery (1) comprising a battery case (2) for accommodating an electrode plate group (3) and an electrolyte, with one open end of the battery case (2) being sealed with an assembled sealing plate (11) that accommodates a safety mechanism (17) for exhausting pressure in the event of pressure build-up in the battery case (2) exceeding a predetermined level, at least one part (13a) of vent holes (13a, 13b, 13c) in the assembled sealing plate (11) facing the inside of the battery case (2) is constituted of an aperture that results from formation of a turned-out portion (23), the distal end of the turned-out portion (23) being allowed to abut on an insulating plate (4a) that makes contact with one end of the electrode plate group (3) so as to restrict movement of the electrode plate group (3). This can prevent malfunctioning due to displacement of the electrode plate group (3) when an impact or vibration is applied.