A wafer storing, closed container for use in a clean room of a semiconductor manufacturing system is provided with an attached inert gas tank so as to eliminate the need to convey the container to an inert gas purge station to supplement the inert gas supply in the container due to leakage. A gas passageway is formed in a body of the container in such a manner that one end thereof is open inside the container. The other end is open outside the container. The portable inert gas tank is detachably connected to the other end of the gas passageway so as to automatically supplement the container with the inert gas.