OPERATING METHOD OF FUEL CELL SYSTEM

A method of operating a fuel cell system which has a plurality of fuel cell stacks, and includes a first refrigerant passage, a second refrigerant passage, a first temperature acquisition unit, a second temperature acquisition unit, a first refrigerant circulation passage, a first refrigerant pumping unit, a first heat exchanger and a first flow rate adjusting valve includes: after the plurality of fuel cell stacks are stopped, until a predetermined condition is satisfied, driving the first refrigerant pumping unit; and causing the first flow rate adjusting valve to adjust the flow rate of the refrigerant flowing through the first refrigerant passage and the flow rate of the refrigerant flowing through the second refrigerant passage, on the basis of the temperature of the refrigerant flowing through each of the first refrigerant passage and the second refrigerant passage acquired by the first temperature acquisition unit and the second temperature acquisition unit.