To provide a duct storage box capable of preventing inflow of extra air to air supply ducts.

The duct storage box 10A includes: a louver 12 mounted to an opening 16 of a wall 15 partitioning inside and outside of a plant; and a chamber 13 which is continued to the louver 12 and installed on the inner side of the wall 15 and to which extension ends 22 of the air supply ducts 11 of an air supply device for sending air to a clean room are connected. The chamber 13 is formed by top and bottom walls 17, 18, both sidewalls 19, 20 and a rear wall 21 opposing to the louver 12. A first air exhaust unit 29 including a check valve damper 28A for discharging air within the chamber 13 to outside of the chamber 13 in accordance with pressure of air entered from the louver 12 to the chamber 13 is installed on the rear wall 21.