A battery chamber is formed inside a sealed container. A module battery and a charging/discharging path outside a battery are housed in the battery chamber. In the module battery, an electric cell chamber and an air chamber are formed inside a heat-insulating container. The electric cell chamber and the air chamber are divided by a heat transfer wall. An electric cell of a sodium-sulfur battery, and a charging/discharging path inside a battery are housed in the electric cell chamber. An intake path starts from outside of the sealed container and leads to the air chamber. An exhaust path starts from the air chamber and leads to the sealed container. The blower generates an air flow that sequentially flows through the intake path, the air chamber and the exhaust path. In a case where the cooling of the electric cell chamber is required, the air flow is generated.