A continuous nitriding treatment furnace includes a nitriding chamber, a heater, a first nitriding zone, and a second nitriding zone lower in atmosphere gas temperature than the first nitriding zone by 25° C. to 150° C., the continuous nitriding treatment furnace being configured such that an atmosphere gas in the first nitriding zone flows into the second nitriding zone and being configured to execute a nitriding treatment that forms an iron nitride compound layer composed of an ε phase or of the ε phase and a γ′ phase on a surface of the steel member in the first nitriding zone and precipitates the γ′ phase in the iron nitride compound layer in the second nitriding zone.