A method of forming a dielectric film by an organic metal CVD method, comprising the step of supplying an organic metal compound into a treating container having a substrate to be treated held therein to form the dielectric film on the substrate, wherein the dielectric film forming step comprises the first step of depositing, in the treating container, the dielectric film under a first condition so set as to allow the residence time of the organic metal compound to extend to a first value, and the second step of further depositing, after the first step and in the treating container, the dielectric film under a second condition so set as to allow the residence time of the organic metal compound to extend to a second value smaller than the first value.