To provide an apparatus and a method for manufacturing a reducing gas being used in the treating step of a metal and the like under a reducing atmosphere where ammonia being dangerous and inconvenient for handling is not used, where the mixing of oxygen gas lowering the quality of a treating matter by oxidation is prevented and where moisture causing the generation of oxygen by pyrolysis in the treating step is not involved.

The apparatus for manufacturing the reducing gas comprises an on-site hydrogen producing apparatus in which hydrogen gas is produced from a hydrocarbon as a raw material, an on-site nitrogen producing apparatus in which nitrogen gas is produced, a concentration regulating apparatus for the hydrogen gas and the nitrogen gas generated in the producing apparatuses and a deoxigenation apparatus and a moisture removing apparatus for a regulated mixed gas.