A method includes an in-stop-mode power generating process of, if an instruction to stop an operation of a fuel cell is detected, stopping supply of a fuel gas, and supplying an oxide gas to the fuel cell to generate power from an oxide-gas supply apparatus, and then stopping power generation of the fuel cell, and a gas replacing process of, after the power generation of the fuel cell is stopped, activating the gas replacement apparatus at a predetermined timing to supply a replacement gas to the anode side of the fuel cell to replace the fuel gas on the anode side with the replacement gas.