PURPOSE: To form a metallic film having excellent reliability without attacking a metallic substrate in the stage of forming the metallic film on said substrate by using a transition metallic compd. having sandwich structure as a gaseous raw material for forming the metallic film.

CONSTITUTION: A vessel 6 contg. a compd. having the sandwich structure in which a transition metal such as Mo or the like is sandwiched between the two faces arranged annularly with carbon and hydrogen atoms, such as bis-benzene molybdenum (Mo(C6H6)2) as a raw material is put into a thermostatic chamber 7. The above-mentioned Mo compd. is heated to about 200°C to form a gas in the chamber 7 which the gas is supplied together with a carrier gas such as H2, Ar or the like and a gas for dilution from conduits 8, 9 into a reaction chamber 1 through a pipe 10. The inside of the chamber 1 is heated to 200W600°C by a heater 4 and Mo(C6H6)2 is thermally decomposed and the uniform film of Mo having high reliability is formed on the surface of a substrate 12 consisting of a semiconductor, etc. on a holder 13.