PURPOSE: To efficiently supply film forming gases contg. oxygen active species without depending on a substrate temp. by heating the gases flowing in a gas introducing pipe in a heater section to form the active species of the oxygen system.

CONSTITUTION: The film forming gases, such as gaseous N2O, from a gas supplying source in the outside of a film forming chamber 10 are introduced into the chamber via the gas introducing pipe 12. The heater section 20 is provided in the front end part of the pipe 12 in this film forming chamber 10 to heat the gases via heater wires. The gases, such as N2O, are cracked at about 600 to 700°C to form the active oxygen in this way. The active species of the oxygen obtd. in such a manner are supplied form the front end of the introducing pipe 12 toward the substrate surface to form the film. The temp. rise of the substrate and the film forming chamber wall 10a is preferably prevented by providing a cooling cover 24 in the front end part of the pipe 12 and a cooling mechanism 28 in the introducing part of the film forming chamber 12, respectively. The active oxygen is effectively supplied onto the surface of the substrate under film formation without depending on the substrate temp. in this way.