A film formation method is disclosed for depositing a metal film on a target substrate by supplying a metal carbonyl source in gas phase to a surface of the target substrate and decomposing the source near the surface of the target substrate. The method includes a step of preferentially decomposing the metal carbonyl source in an area near the outer peripheral portion of the target substrate when the metal film is being deposited on the surface of the target substrate. As a result, a CO concentration in the atmosphere is increased locally near the outer peripheral portion of the target substrate and the depositing of the metal film on the outer peripheral portion is better controlled.