A hydrogen production apparatus, which is provided in a power generation plant comprising a boiler and a steam turbine that is driven by a high-temperature steam produced in the boiler, and which produces steam for supply to other apparatus within the power generation plant, the hydrogen production apparatus comprising: a humidifier, which is supplied with a process fluid containing carbon monoxide, and mixes the process fluid with a steam, a reactor, which reacts a humidified process fluid output from the humidifier in presence of a catalyst, thereby converting the carbon monoxide within the process fluid into carbon dioxide, and which increases the amount of hydrogen contained in the process fluid, a first pipe through which a high-temperature process fluid flows following reaction in the reactor, a second pipe that supplies a makeup water, at least one first heat exchanger (51a, 51b), wherein each of it is disposed at one location of one or more locations where the first pipe and the second pipe cross each other, and raises the temperature of the makeup water flowing through the second pipe by heat exchange with the high-temperature process fluid flowing through the first pipe, a discharge passage through which a portion of excess moisture within the humidifier is released externally, a second heat exchanger which is provided at a location where the second pipe and the discharge passage cross each other, and which raises the temperature of the makeup water flowing through the second pipe by heat exchange with the discharge water flowing through the discharge passage, a gas-liquid separator which is supplied with makeup water heated by the first heat exchanger and the second heat exchanger, a third pipe which is connected to a gas phase portion of the gas-liquid separator, and supplies a steam separated by the gas-liquid separator to the other apparatus, wherein the other apparatus is an apparatus such as a desulfurizer within the power generation plant which requires high-temperature steam as a heat source. a humidifier, which is supplied with a process fluid containing carbon monoxide, and mixes the process fluid with a steam, a reactor, which reacts a humidified process fluid output from the humidifier in presence of a catalyst, thereby converting the carbon monoxide within the process fluid into carbon dioxide, and which increases the amount of hydrogen contained in the process fluid, a first pipe through which a high-temperature process fluid flows following reaction in the reactor, a second pipe that supplies a makeup water, at least one first heat exchanger (51a, 51b), wherein each of it is disposed at one location of one or more locations where the first pipe and the second pipe cross each other, and raises the temperature of the makeup water flowing through the second pipe by heat exchange with the high-temperature process fluid flowing through the first pipe, a discharge passage through which a portion of excess moisture within the humidifier is released externally, a second heat exchanger which is provided at a location where the second pipe and the discharge passage cross each other, and which raises the temperature of the makeup water flowing through the second pipe by heat exchange with the discharge water flowing through the discharge passage, a gas-liquid separator which is supplied with makeup water heated by the first heat exchanger and the second heat exchanger, a third pipe which is connected to a gas phase portion of the gas-liquid separator, and supplies a steam separated by the gas-liquid separator to the other apparatus, wherein the other apparatus is an apparatus such as a desulfurizer within the power generation plant which requires high-temperature steam as a heat source.