A fuel cell system comprising: a fuel cell stack formed by stacking a plurality of fuel cells for generating electrical energy by electrochemical reactions of a fuel gas and an oxygen-containing gas; a heat exchanger for raising a temperature of the oxygen-containing gas by heat exchange with a combustion gas, and supplying the oxygen-containing gas to the fuel cell stack; a combustion apparatus including an exhaust gas combustor for combusting the fuel gas discharged from the fuel cell stack as a fuel exhaust gas and the oxygen-containing gas discharged from the fuel cell stack as an oxygen-containing exhaust gas to produce the combustion gas; and a control device for controlling an amount of the electrical energy generated in the fuel cell stack, wherein the control device includes: a combustion apparatus temperature comparison unit for comparing a temperature of the exhaust gas combustor during power generation of the fuel cell stack and a predetermined combustion apparatus temperature range; and a combustion apparatus flame-out determination unit for determining whether flame-out occurs in the exhaust gas combustor based on a comparison result by the combustion apparatus temperature comparison unit; characterized in that the combustion apparatus further includes a start-up combustor for combusting the fuel gas or raw fuel to be reformed into the fuel gas and the oxygen-containing gas to produce the combustion gas; and that the control device further includes: a combustion apparatus control unit for starting operation of the start-up combustor when the combustion apparatus flame-out determination unit determines that flame-out has occurred in the exhaust gas combustor. a fuel cell stack formed by stacking a plurality of fuel cells for generating electrical energy by electrochemical reactions of a fuel gas and an oxygen-containing gas; a heat exchanger for raising a temperature of the oxygen-containing gas by heat exchange with a combustion gas, and supplying the oxygen-containing gas to the fuel cell stack; a combustion apparatus including an exhaust gas combustor for combusting the fuel gas discharged from the fuel cell stack as a fuel exhaust gas and the oxygen-containing gas discharged from the fuel cell stack as an oxygen-containing exhaust gas to produce the combustion gas; and a control device for controlling an amount of the electrical energy generated in the fuel cell stack, wherein the control device includes: a combustion apparatus temperature comparison unit for comparing a temperature of the exhaust gas combustor during power generation of the fuel cell stack and a predetermined combustion apparatus temperature range; and a combustion apparatus flame-out determination unit for determining whether flame-out occurs in the exhaust gas combustor based on a comparison result by the combustion apparatus temperature comparison unit; a combustion apparatus temperature comparison unit for comparing a temperature of the exhaust gas combustor during power generation of the fuel cell stack and a predetermined combustion apparatus temperature range; and a combustion apparatus flame-out determination unit for determining whether flame-out occurs in the exhaust gas combustor based on a comparison result by the combustion apparatus temperature comparison unit; characterized in that the combustion apparatus further includes a start-up combustor for combusting the fuel gas or raw fuel to be reformed into the fuel gas and the oxygen-containing gas to produce the combustion gas; and that the control device further includes: a combustion apparatus control unit for starting operation of the start-up combustor when the combustion apparatus flame-out determination unit determines that flame-out has occurred in the exhaust gas combustor. a combustion apparatus control unit for starting operation of the start-up combustor when the combustion apparatus flame-out determination unit determines that flame-out has occurred in the exhaust gas combustor.