TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Components: The fuel cell system further comprises an auxiliary humidifier controlled by the control unit, and collecting water contained in the remaining fuel gas that has passed through the fuel gas humidifier and in the remaining oxidation gas that has passed through the oxidation gas humidifier. The auxiliary humidifier humidifies the fuel gas that is supplied to the fuel cell stack from the fuel gas supply unit and the oxidation gas that is supplied to the fuel cell stack from the oxidation gas supply unit. It comprises remaining exhaust condensation unit for condensing the remaining fuel gas that has passed through the fuel gas humidifier and the remaining oxidation gas that has passed through the oxidation gas humidifier; water storage unit for receiving and storing water generated by the remaining exhaust condensation unit; first injector for injecting water stored in the water storage unit into the fuel gas supplied to the fuel cell stack from the fuel gas supply unit; and second injector for injecting water stored in the water storage unit into the oxidation gas supplied to the fuel cell stack from the oxidation gas supply unit. It further comprises an electric heater for heating water stored in the water storage unit. The electric heater is controlled to operate for a predetermined time if an ambient temperature is lower than a predetermined temperature. The injectors have ultrasonic nozzles, and are controlled to operate for a predetermined time after commencing operation of the fuel cell stack. The remaining exhaust gas condensation unit comprises first condenser condensing the remaining fuel gas that has passed through the fuel gas humidifier; second condenser condensing the remaining oxidation gas that has passed through the oxidation gas humidifier; radiator cooling a coolant that has passed through the two condensers; coolant circulating passage connecting the two condensers and the radiator such that the coolant circulates through the two condensers and the radiator; and coolant pump disposed in coolant circulating passage and pumping the coolant such that coolant that has passed through the radiator is supplied to the fuel cell stack, two condensers, and then back to radiator.