A fuel cell system comprising: a fuel cell having a membrane electrode assembly provided with an electrolyte and a cathode and anode respectively arranged at two sides of the electrolyte and an oxidizing gas passage configured to feed an oxidizing gas to the cathode, the cathode including a conductive material (2c1), catalyst (2c3), and ionomer (2c2) which covers the conductive material (2c1) and catalyst (2c3); an oxidizing gas feed path connected to an inlet of the oxidizing gas passage; an oxidizing gas feeder arranged in the oxidizing gas feed path and configured to feed oxidizing gas to the cathode; a voltmeter between the anode and cathode configured to detect an output voltage value of the cell; and a system controller configured to control the fuel cell system to make an output current value of the fuel cell equal to a target current value which is determined based on a target power generation quantity of the fuel cell; characterized in that the fuel cell system further comprises: an electrical resistance meter between the anode and cathode configured to detect an electrical resistance value; wherein: the system controller is configured to: if the output voltage value of the fuel cell is lower than a predetermined threshold voltage value and the electrical resistance value of the fuel cell is higher than a predetermined threshold resistance value, control the oxidizing gas feeder to perform control for increasing an oxidizing gas amount which increases an amount of oxidizing gas sent to the fuel cell; and stop the control for increasing the oxidizing gas amount if the electrical resistance value of the cell becomes higher than a predetermined upper limit resistance value during the control for increasing the oxidizing gas amount. a fuel cell having a membrane electrode assembly provided with an electrolyte and a cathode and anode respectively arranged at two sides of the electrolyte and an oxidizing gas passage configured to feed an oxidizing gas to the cathode, the cathode including a conductive material (2c1), catalyst (2c3), and ionomer (2c2) which covers the conductive material (2c1) and catalyst (2c3); an oxidizing gas feed path connected to an inlet of the oxidizing gas passage; an oxidizing gas feeder arranged in the oxidizing gas feed path and configured to feed oxidizing gas to the cathode; a voltmeter between the anode and cathode configured to detect an output voltage value of the cell; and a system controller configured to control the fuel cell system to make an output current value of the fuel cell equal to a target current value which is determined based on a target power generation quantity of the fuel cell; characterized in that the fuel cell system further comprises: an electrical resistance meter between the anode and cathode configured to detect an electrical resistance value; wherein: an electrical resistance meter between the anode and cathode configured to detect an electrical resistance value; wherein: the system controller is configured to: if the output voltage value of the fuel cell is lower than a predetermined threshold voltage value and the electrical resistance value of the fuel cell is higher than a predetermined threshold resistance value, control the oxidizing gas feeder to perform control for increasing an oxidizing gas amount which increases an amount of oxidizing gas sent to the fuel cell; and stop the control for increasing the oxidizing gas amount if the electrical resistance value of the cell becomes higher than a predetermined upper limit resistance value during the control for increasing the oxidizing gas amount. if the output voltage value of the fuel cell is lower than a predetermined threshold voltage value and the electrical resistance value of the fuel cell is higher than a predetermined threshold resistance value, control the oxidizing gas feeder to perform control for increasing an oxidizing gas amount which increases an amount of oxidizing gas sent to the fuel cell; and stop the control for increasing the oxidizing gas amount if the electrical resistance value of the cell becomes higher than a predetermined upper limit resistance value during the control for increasing the oxidizing gas amount.