Abstract: A fuel cell power generating apparatus using a fuel cell (10) having a structure such that a cathode and an anode are disposed on opposite sides of a polymer electrolyte membrane, comprising: an air introduction passage (11) for introducing air to the cathode; an air discharge passage (15) for discharging, to the outside of the system, discharge gas containing reactant water generated at the cathode; a circulation passage (16) connected between the air discharge passage and the air introduction passage in order to again introduce at least a portion of the discharge gas flowing through the air discharge passage to the air introduction passage and thus to the cathode; a valve (17) provided for at least one of the air introduction passage and the air discharge passage; a temperature sensor (22) for measuring the temperature of the discharge gas from the cathode; an ampere meter (19) for measuring the level of an electric current output from the fuel cell; and a control unit (18) for controlling the degree of ope