The fuel cell system is equipped with a fuel cell for generating power by chemically reacting a fuel gas supplied to an anode and an oxygen containing gas supplied to a cathode; an anode off-gas discharge mechanism for discharging an anode off-gas from the anode; a combustion heater for combusting a combustion gas; a dilution mechanism for diluting the anode off-gas by the oxygen containing gas; a first path for introducing the anode off-gas into the combustion heater; a first flow rate adjustment mechanism for adjusting an introduction amount of the anode off-gas into the first path; a second path for introducing the anode off-gas into the dilution mechanism; a second flow rate adjustment mechanism for adjusting an introduction amount of the anode off-gas into the second path; and a control mechanism for controlling actuations of the first flow rate adjustment mechanism and the second flow rate adjustment mechanism.