NOVELTY - A fuel-cell power-generating device consists of a fuel generator (35), an oxidizing-agent supplier, and a fuel cell. The device has a cell stack (38) formed by laminating two or more fuel cells, and gas-cleaning portion (32) for removing impurities from the source gas. A purge path is provided for purging the gas remaining in the cell stack with source gas. Gas-cleaning portion (84) is provided for removing impurities from source gas. The device restores removal performance while gas-cleaning portion (84) is not purged.    USE - Fuel-cell power-generating device is used for domestic cogeneration systems, portable apparatuses, and electric vehicles.    ADVANTAGE - The fuel-cell power-generating device efficiently purifies impurities contained in purge gas, and maintains high electric-power generation efficiency for a long period of time.    DETAILED DESCRIPTION - A fuel-cell power-generating device consists of a fuel generator (35) for producing fuel gas from source gas, an oxidizing-agent supplier, and a fuel cell for generating electric power from the fuel gas and oxidizing-agent gas. The device has a cell stack (38) formed by laminating two or more fuel cells, and gas-cleaning portion (32) for removing impurities from the source gas to prevent bad influence on fuel generator. A purge path is provided for purging the gas remaining in the cell stack with source gas before and/or after start of electric-power generation. Gas-cleaning portion (84) is provided for removing impurities from the source gas to prevent bad influence on cell stack. The device restores removal performance while gas-cleaning portion (84) is not purged. Gas-cleaning portion (84) comprises activated carbon having a mean pore diameter of 1.5-2.5 nm, or noble metals supported and adsorbed in inorganic porous component containing aluminum and silicon. An INDEPENDENT CLAIM is included for operating method of fuel-cell power-generating device.    DESCRIPTION OF DRAWING(S) - The drawing shows a structural view of the fuel-cell power-generating device. (Drawing includes non-English language text)    Gas-cleaning portions (32,84)    Fuel generator (35)    Cell stack (38)    Blower (39)    Humidifier (41)