To prevent a foreign material from adhering to the outer peripheral face of an inner tube in a CVD device.

The CVD device is provided with the inner tube 2 forming a processing chamber 4, an outer tube 3 surrounding the inner tube 2, a heater unit 20 heating the inner part of the outer tube 3, a boat 11 holding a plurality of wafers 10 and carrying them into the processing chamber 4, a gas introduction nozzle 22 introducing material gas 30 into the processing chamber 4, and an exhaust slit 25 which is arranged in the tube wall of the inner tube 2 and exhausts the processing chamber 4. A nitrogen gas supply nozzle 26 jetting nitrogen gas 31 in a circumferential direction is vertically disposed in a clearance 5 between the inner tube 2 and the outer tube 3. Since diffusion of processing gas exhausted to the clearance from the exhaust slit can be inhibited in the clearance by filling the clearance with nitrogen gas, deposition of the foreign material on the outer peripheral face of the inner tube can be prevented, and occurrence of particles with deposition can previously be prevented.