It is aimed to provide a battery pack capable of securing safety by preventing A battery contained in the battery pack from entering a burning state even if the battery releases high-temperature gas in an abnormal state. An exhaust duct 1C for permitting the flow of gas released from the battery is provided and the gas is exhausted to the outside after reducing the temperature thereof in the exhaust duct 1C. A flow passage area of the exhaust duct 1C is in the range of not less than 0.5 mm.sup.2 and not more than 15 mm.sup.2 per 1 Ah of the battery capacity. The exhaust duct 1C is provided with a gas cooling portion 1L and a spark trapping portion 1M.