A film formation method includes setting a target object at a temperature of 150 to 550° C., the target object being placed inside the process container configured to hold a vacuum state therein, and then, repeating a cycle alternately including a first supply step and a second supply step a plurality of times to form a silicon nitride film on the target object. The first supply step is a step of supplying monochlorosilane gas as an Si source into the process container while setting the process container at a pressure of 66.65 to 666.5 Pa therein. The second supply step is a step of supplying a nitrogen-containing gas as a nitriding gas into the process container.