NOVELTY - The fuel cell power-generating device (50) has fuel reformer (22) comprising water vapor-supply unit, reformer (3), carbon-monoxide transformer (4), and carbon monoxide removal unit (5), and fuel cell (6), and temperature/humidity controller (15) to measure dew point of fuel gas, between fuel reformer and fuel cell. The flow rate of water vapor supplied from supply unit is controlled to instructed value so as to obtain dew point.    USE - As fuel cell power generating device e.g. polymer electrolyte fuel cell.    ADVANTAGE - The fuel cell power-generating device has stable electric power generating efficiency, and accurately controls dew point of fuel gas and humidification amount of reactive gas, without using heat exchanger, water vapor generator and mixer.    DETAILED DESCRIPTION - The fuel cell power generating device (50) has a fuel reformer (22) comprising a water vapor-supply unit to supply water, a reformer (3) to produce hydrogen-rich reformed gas from water vapor and original fuel, a carbon-monoxide transformer (4) to transform carbon monoxide and water vapor into reformed gas, and a carbon monoxide removal unit (5) to add air to reformed gas supplied by carbon-monoxide converter, transform carbon monoxide into carbon dioxide by carbon monoxide selective reactive reaction and generate fuel gas, fuel cell (6) to generate electric power using the fuel gas having hydrogen modified by fuel reformer, and a temperature/humidity controller (15) to measure the dew point of fuel gas, provided between fuel reformer and fuel cell. The flow rate of water vapor supplied from water-vapor supply unit is controlled to instructed value so that dew point is obtained.    DESCRIPTION OF DRAWING(S) - The figure shows the profile of structure of the fuel cell power-generating device. (Drawing includes non-English language text).    reformer (3)    carbon monoxide transformer (4)    carbon monoxide removal unit (5)    fuel cell (6)    temperature/humidity controller (15)    fuel reformer (22)    fuel cell power generating device (50)