Provided is a substrate processing apparatus that can suppress the amount of inert gas and dry gas used and also can prevent reductions in throughput. A substrate processing apparatus is provided with: a loader module; an opener that removes a cover from a FOUP having a main body, an opening and the cover, to communicate the inside of the FOUP with the inside of the loader module through the opening; an N2 gas supply unit that is attached to the loader module and supplies N2 gas to the inside of the FOUP; and two slide cover plates movable respectively along an opening surface of the opening. The slide cover plates move toward each other until the gap therebetween is 1 mm to 3 mm to shield the opening of the FOUP that is attached to the loader module from the inside of the loader module.