A technique for effectively suppressing the generation of particles resulting from peeling-off of unnecessary films that have unavoidably adhered to the inner surface of the reaction tube of an ALD film-forming apparatus during a film formation process for forming a film on a semiconductor substrate. A precoating process utilizing ALD is performed to deposit a metal oxide film, e.g., an aluminum oxide film, onto the unnecessary films, in order to prevent peeling-off of the unnecessary films. Ozone is supplied, as a precoat gas, into the reaction tube during the precoating process by a nozzle of a different type and/or position from that of the nozzle for supplying ozone, as a film-forming gas, into the reaction tube during the film formation process.