A method for depositing a silicon nitride film is provided. A silicon nitride film is deposited in a depression formed in a surface of a substrate from a bottom surface and a lateral surface by ALD toward a center of the depression in a lateral direction so as to narrow a space at the center of the depression. First nitrogen radicals are adsorbed into the depression immediately before a stage of filling the space at the center with the silicon nitride film deposited toward the center of the depression. A silicon-containing gas is adsorbed on the first nitrogen radical in the depression by physical adsorption. Second nitrogen radicals are supplied into the depression so as to release the silicon-containing gas from the first nitrogen radical and to cause the released silicon-containing gas to react with the second nitrogen radical, thereby depositing a silicon nitride film to fill the central space.