A component box has a shape of a substantially flat plate, and is stacked along a direction UPR toward the ceiling of a vehicle with its center placed at a central portion of a casing for a battery pack. Cooling wind which has been used for air-conditioning inside the vehicle and supplied from a cooling fan to the battery pack is supplied to a coolant introducing space located on an upper side of a module, passes through a gap between adjacent battery groups to flow down to a lower side of the battery groups, and then is emitted from a coolant lead-out space located at a lower side of the module out of the battery pack. Since the component box is in contact with a cooling wind passage with the casing therebetween, the component box in contact with the cooling wind via the casing is cooled down simultaneously with the cooling of the module. Since the component box is placed with its center positioned at the central portion of the battery pack, variations in temperature among batteries can be suppressed.