METHOD FOR OPERATING FUEL CELL SYSTEM AND FUEL CELL SYSTEM

There is provided a method for operating a fuel cell system and the fuel cell system which allow a required output to be efficiently obtained. A method for operating a fuel cell system including: a fuel cell stack (101); and an accessory group constituted of, at least, a fuel gas supply means for supplying a fuel gas to the fuel cell stack (101), an air supply means for supplying air to the fuel cell stack (101), a cooling water supply means for supplying a cooling water to the fuel cell stack (101), and a radiator (106) for performing heat exchange with the cooling water, the method includes: when a current output current is increased to a target output current (201), a step of increasing an output current (204) while leaving at least one accessory power of the accessory group in a state lower than accessory power according to the target output current (202); and a step of thereafter increasing the accessory power in the state lower than the accessory power according to the target output current to the accessory power according to the target output current (206).