A battery case for mounting under a floor of a vehicle comprises a case body containing a battery module and a cover for closing over an opening of the case body. A reinforcement member for reinforcing the case body is attached to an outer surface of the case body. The case body is provided with a gas circulation hole for letting a gas flow from within the case body into the reinforcement member. The reinforcement member is provided with a gas exhaust port for letting out the gas having flown into the reinforcement member.
