There is provided a method for forming a nitride film on a substrate to be processed by a thermal ALD which repeats: supplying a film forming raw material gas to the substrate to be processed while heating the substrate to be processed to a predetermined temperature; and supplying a nitriding gas to the substrate to be processed, the nitride film forming method comprises supplying a chlorine-containing gas to the substrate to be processed after the supplying the film forming raw material gas.