A substrate storage container includes a container body for accommodating and aligning semiconductor wafers, a door which opens and closes the front of the container body and a pair of valve units disposed at the bottom of the container body for controlling gas flow. Each valve unit includes a fixed sleeve for gas flow, fitted in a rib of a through-hole of the container body, a holding sleeve fitted in the through-hole of the container body with an o-ring interposed therebetween and mated and threaded with the fixed sleeve, a check valve built between the fixed sleeve and the holding sleeve, leaving a clearance, an elastically deformable element for opening and closing the check valve, an interior lid sleeve for gas flow, opposing the check valve and supporting the elastically deformable element, and a filter interposed between the holding sleeve and the interior lid sleeve.