A method includes predicting, while fuel cell system is operated, whether or not the outside temperature becomes equal to or less than a first predetermined temperature; performing, when it is predicted that the outside temperature becomes equal to or less than the first predetermined temperature, residual water scavenging processing on only an oxidizer gas supply/discharge mechanism and thereafter stopping the operation of the fuel cell system; predicting, after the stop of the operation of the fuel cell system, whether or not the temperature of a predetermined component included in the fuel cell system becomes equal to or less than a second predetermined temperature; and performing the residual water scavenging processing on the fuel gas supply/discharge mechanism when it is predicted that the temperature of the predetermined component becomes equal to or less than the second predetermined temperature.