An oxide film is formed on a target substrate by CVD, in a process field to be selectively supplied with a first process gas including a source gas containing a film source element and no amino group, a second process gas including an oxidizing gas, and a third process gas including a preliminary treatment gas. A first step includes an excitation period of supplying the third process gas excited by an exciting mechanism, thereby performing a preliminary treatment on the target substrate by preliminary treatment gas radicals. A second step performs supply of the first process gas, thereby adsorbing the film source element on the target substrate. A third step includes an excitation period of supplying the second process gas excited by an exciting mechanism, thereby oxidizing the film source element adsorbed on the target substrate by oxidizing gas radicals.