A lamination molding apparatus which can lower the oxygen concentration in a molding room in short time is provided. A lamination molding apparatus, including a molding room; a processing head; a driving device housing room housing a driving device moving the processing head; a partitioning section to partition the molding room from the driving device housing room; a discharging section to discharge gas in the molding room; and an inert gas supplying apparatus to supply the inert gas to both of the molding room and to the driving device housing room.