NOVELTY - A fuel cell system (1) contains hydrogen generating apparatus (4) which generates reducing agent gas containing hydrogen by steam reforming reaction from source gas and water, burner (18) which produces heat required for steam reforming reaction by combustion, air supply apparatus (5) which supplies oxidizing agent gas, fuel cell which carries out electrochemical reaction of reducing agent gas and oxidizing agent gas to generate electric power, and condenser (8) which condenses moisture content in waste gas component of e.g. reducing agent waste gas after reaction discharged from fuel cell.    USE - A fuel cell system used as domestic fuel battery co-generation system.    ADVANTAGE - Flow volume of condensed water feed pump can be controlled to an appropriate range, and fuel cell system can be simplified while achieving cost reduction.    DETAILED DESCRIPTION - A fuel cell system (1) comprises hydrogen generating apparatus (4) which generates reducing agent gas containing hydrogen by steam reforming reaction from source gas and water, burner (18) which produces heat required for steam reforming reaction by combustion, air supply apparatus (5) which supplies oxidizing agent gas, fuel cell which carries out electrochemical reaction of reducing agent gas and oxidizing agent gas to generate electric power, condenser (8) which condenses moisture content in waste gas component of reducing agent waste gas after reaction discharged from fuel cell, oxidizing agent waste gas, and/or combustion exhaust gas of burner to be recovered as condensed water, condensed water tank (9) which collects condensed water, condensed water supply apparatus sent to pure-water device (10) for carrying out deionization process of condensed water, pure water storage tank (13) which stores pure water generated by pure-water device, pure-water water level detection part (15) which detects water level of pure water storage tank, and controller (14) which controls each apparatus. The controller reduces the operation output of condensed water supply apparatus when the time in which the change of the detected water level during operation of condensed water supply apparatus is shorter than predetermined time and increases operation output when longer than predetermined time.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of the fuel cell system. (Drawing includes non-English language text).    Fuel cell (1)    Hydrogen generating apparatus (4)    Air supply apparatus (5)    Condenser (8)    Condensed water tank (9)    Pure-water device (10)    Pure water storage tank (13)    Controller (14)    Pure-water water level detection part (15)    Burner (18)