The invention relates to an apparatus for producing hydrogen (4) and a fuel battery system (100) including the same. The apparatus for producing hydrogen (4) has a reforming unit (5) wherein a material supplied thereto is subjected to a reforming reaction to give a hydrogen-containing gas, a first gas supplying unit (1) from which a gas containing a nitrogen-containing compound is supplied into the reforming unit (5), a CO removing unit (7) carrying an oxidation catalyst containing an ammonia-poisoning metal wherein carbon monoxide in the hydrogen-containing gas is removed via an oxidation reaction using the oxidation catalyst and an oxidation gas, a second gas supplying unit (3) from which the oxidation gas is supplied to the CO removing unit, and a controlling unit (10), in which the gas containing a nitrogen-containing compound is supplied from the first gas supplying unit to the reforming unit in the course of the reforming reaction as described above; and a fuel battery system (100) provided with the apparatus for producing hydrogen, wherein the controlling unit has such a constitution that the regeneration of the oxidation catalyst is initiated when a parameter correlating to the cumulative supply quantity of ammonia into the CO removing unit attains to a definite threshold.