The present invention relates to a method of forming a metal-nitride film onto a surface of an object to be processed in a processing container in which a vacuum can be created. The method of the invention includes: a step of continuously supplying an inert gas into a processing container set at a low film-forming temperature; and a step of intermittently supplying a metal-source gas into the processing container, during the step of continuously supplying the inert gas. During the step of intermittently supplying the metal-source gas, a nitrogen-including reduction gas is supplied into the processing container at the same time that the metal-source gas is supplied, during a supply term of the metal-source gas. The nitrogen-including reduction gas is also supplied into the processing container for a term shorter than a non-supply term of the metal-source gas, during the non-supply term of the metal-source gas. According to the invention, a metal-nitride film can be deposited whose chlorine density is low, whose resistivity is low, in which less cracks may be generated, and whose abnormal growth may not be generated.