An apparatus for forming a deposited film by introducing two or more kinds of gaseous starting materials for formation of a deposited film and a gaseous halogenic oxidizing agent having the property of oxidation action for said starting materials into a reaction space to effect chemical contact therebetween to thereby form a plural number of precursors including precursors under excited state, and forming a deposited film in a plurality of layers with different compositions on a substrate existing in a film forming space spatially communicated with said reaction space with the use of at least one precursor of the precursors as the feeding source for the constituent element of the deposited film, said apparatus comprising a plural number of gas introducing means of a multiple tubular structure for discharging into said reaction space said gaseous starting materials and said gaseous halogenic oxidizing agent through the discharging outlets, respectively, and permitting them to react with each other to form the precursors and means for preventing contact of precursors unnecessary for the desired film formation of the precursors with the substrate.