NOVELTY - A fuel cell power generating device system comprises hydrogen generating apparatus which generates fuel gas having hydrogen from combustible source gas, stack (9) which generates direct current power using fuel gas and oxidizing agent gas which are generated by hydrogen generating apparatus, waste-heat-recovery unit which circulates water and collects exhaust heat, gas supply control unit which controls supply of source gas by opening and closing valve in gas supply line, housing (8), gas concentration measurement unit, free-air-temperature-indicator measure unit (13) and exhausting unit.    USE - Fuel cell power generating device system for water heater.    ADVANTAGE - The fuel cell power generating device system can be returned safely.    DETAILED DESCRIPTION - A fuel cell power generating device system comprises hydrogen generating apparatus which generates fuel gas having hydrogen as main component from combustible source gas, stack (9) which generates direct current power using fuel gas and oxidizing agent gas which are generated by hydrogen generating apparatus, waste-heat-recovery unit which circulates water and collects exhaust heat at time of electric power generation of stack or exhaust heat at time of electric power generation of stack, gas supply control unit which controls supply of source gas by opening and closing valve in gas supply line, housing (8), gas concentration measurement unit which measures concentration of combustible gas of source gas leaked to space in housing or fuel gas, free-air-temperature-indicator measure unit (13) which measures outside temperature, exhausting unit which exhausts source gas leaked to space in housing or fuel gas out of housing, control unit, first power supply (11) which operates free-air-temperature-indicator measure unit, exhaust unit, gas concentration measurement unit and control unit, and second power supply (12) which operates hydrogen generating apparatus, stack, waste-heat-recovery unit and gas supply control unit.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of the fuel cell power generating device system. (Drawing includes non-English language text).    Housing (8)    Stack (9)    First power supply (11)    Second power supply (12)    Free-air-temperature-indicator measure unit (13)