A hydrogen generator comprising: a raw material supply unit configured to supply a raw gas; a water supply unit configured to supply water; a water evaporation unit connected to the raw material supply unit and the water supply unit and configured to transform supplied water into steam and to mix the steam with the raw gas; a burner connected to a fuel supply unit configured to supply a fuel gas and an air supply unit configured to supply combustion air; a combustion exhaust gas flow channel which is provided on an inner side than the water evaporation unit and through which a combustion exhaust gas from the burner flows; a reforming catalyst layer configured to receive a gas mixture supplied from the water evaporation unit and produce a reformed gas containing hydrogen by steam-reforming reaction of the gas mixture with a reforming catalyst; and a carbon monoxide reduction unit (10, 11) disposed on an outer side than the water evaporation unit and configured to receive the reformed gas and reduce an amount of carbon monoxide contained in the reformed gas, wherein the water evaporation unit comprises a flow channel member provided on an outer side than the combustion exhaust gas flow channel and defining a flow channel through which the raw gas and the water flow, characterized in that the flow channel member of the water evaporation unit comprises double cylinders and a helical partition portion sandwiched between the cylinders, and wherein the carbon monoxide reduction unit comprises a conversion catalyst layer configured to receive the reformed gas and to reduce carbon monoxide in the reformed gas by shift reaction using a conversion catalyst, wherein the conversion catalyst layer is disposed adjacent to an outside of the water evaporation unit, wherein the water evaporation unit is configured such that a pitch of the helical partition portion is smaller in the water evaporation unit adjacent to the upstream portion of the conversion catalyst layer and is greater in the water evaporation unit adjacent to the remaining portion of the conversion catalyst layer, so that the amount of heat exchange between the conversion catalyst layer and the water evaporation unit is higher in the upstream portion of the conversion catalyst layer than in the remaining portion of the conversion catalyst layer. a raw material supply unit configured to supply a raw gas; a water supply unit configured to supply water; a water evaporation unit connected to the raw material supply unit and the water supply unit and configured to transform supplied water into steam and to mix the steam with the raw gas; a burner connected to a fuel supply unit configured to supply a fuel gas and an air supply unit configured to supply combustion air; a combustion exhaust gas flow channel which is provided on an inner side than the water evaporation unit and through which a combustion exhaust gas from the burner flows; a reforming catalyst layer configured to receive a gas mixture supplied from the water evaporation unit and produce a reformed gas containing hydrogen by steam-reforming reaction of the gas mixture with a reforming catalyst; and a carbon monoxide reduction unit (10, 11) disposed on an outer side than the water evaporation unit and configured to receive the reformed gas and reduce an amount of carbon monoxide contained in the reformed gas, wherein the water evaporation unit comprises a flow channel member provided on an outer side than the combustion exhaust gas flow channel and defining a flow channel through which the raw gas and the water flow, characterized in that the flow channel member of the water evaporation unit comprises double cylinders and a helical partition portion sandwiched between the cylinders, and wherein the carbon monoxide reduction unit comprises a conversion catalyst layer configured to receive the reformed gas and to reduce carbon monoxide in the reformed gas by shift reaction using a conversion catalyst, wherein the conversion catalyst layer is disposed adjacent to an outside of the water evaporation unit, wherein the water evaporation unit is configured such that a pitch of the helical partition portion is smaller in the water evaporation unit adjacent to the upstream portion of the conversion catalyst layer and is greater in the water evaporation unit adjacent to the remaining portion of the conversion catalyst layer, so that the amount of heat exchange between the conversion catalyst layer and the water evaporation unit is higher in the upstream portion of the conversion catalyst layer than in the remaining portion of the conversion catalyst layer.