A fuel cell system, comprising: a fuel cell including an anode and a cathode and generating electricity by a fuel and an oxidant gas respectively supplied to the anode and the cathode; a reforming portion generating the fuel by a source material and water to supply the fuel to the fuel cell; a combustion portion burning an anode-off gas from the fuel cell and a cathode-off gas from the fuel cell to heat the reforming portion; a casing formed by an insulating material and accommodating therewithin the fuel cell, the reforming portion, and the combustion portion; a supply device supplying the source material; a flow sensor detecting a supply flow rate of the source material; a temperature sensor detecting a temperature of the combustion portion; and a control device controlling the supply device, the control device comprising: a temperature obtaining means (step 304, steps 320, 322, 324) for obtaining the temperature of the combustion portion by controlling the supply device to supply the source material at a constant supply flow rate, the temperature being detected by the temperature sensor during a period in which the temperature is stable; a temperature deviation obtaining means (step 404) for obtaining a temperature deviation of the combustion portion, the temperature deviation being a difference between a reference temperature of the combustion portion and the temperature of the combustion portion obtained by the temperature obtaining means (step 304, steps 320, 322, 324); a supply flow rate deviation obtaining means (step 406) for obtaining a deviation of the supply flow rate of the source material from the temperature deviation of the combustion portion obtained by the temperature deviation obtaining means (step 404); and an adjustment means (step 410) for adjusting the supply flow rate of the source material obtained by the flow sensor, on the basis of the deviation of the supply flow rate obtained by the supply flow rate deviation obtaining means (step 406). a fuel cell including an anode and a cathode and generating electricity by a fuel and an oxidant gas respectively supplied to the anode and the cathode; a reforming portion generating the fuel by a source material and water to supply the fuel to the fuel cell; a combustion portion burning an anode-off gas from the fuel cell and a cathode-off gas from the fuel cell to heat the reforming portion; a casing formed by an insulating material and accommodating therewithin the fuel cell, the reforming portion, and the combustion portion; a supply device supplying the source material; a flow sensor detecting a supply flow rate of the source material; a temperature sensor detecting a temperature of the combustion portion; and a control device controlling the supply device, the control device comprising: a temperature obtaining means (step 304, steps 320, 322, 324) for obtaining the temperature of the combustion portion by controlling the supply device to supply the source material at a constant supply flow rate, the temperature being detected by the temperature sensor during a period in which the temperature is stable; a temperature deviation obtaining means (step 404) for obtaining a temperature deviation of the combustion portion, the temperature deviation being a difference between a reference temperature of the combustion portion and the temperature of the combustion portion obtained by the temperature obtaining means (step 304, steps 320, 322, 324); a supply flow rate deviation obtaining means (step 406) for obtaining a deviation of the supply flow rate of the source material from the temperature deviation of the combustion portion obtained by the temperature deviation obtaining means (step 404); and an adjustment means (step 410) for adjusting the supply flow rate of the source material obtained by the flow sensor, on the basis of the deviation of the supply flow rate obtained by the supply flow rate deviation obtaining means (step 406). a temperature obtaining means (step 304, steps 320, 322, 324) for obtaining the temperature of the combustion portion by controlling the supply device to supply the source material at a constant supply flow rate, the temperature being detected by the temperature sensor during a period in which the temperature is stable; a temperature deviation obtaining means (step 404) for obtaining a temperature deviation of the combustion portion, the temperature deviation being a difference between a reference temperature of the combustion portion and the temperature of the combustion portion obtained by the temperature obtaining means (step 304, steps 320, 322, 324); a supply flow rate deviation obtaining means (step 406) for obtaining a deviation of the supply flow rate of the source material from the temperature deviation of the combustion portion obtained by the temperature deviation obtaining means (step 404); and an adjustment means (step 410) for adjusting the supply flow rate of the source material obtained by the flow sensor, on the basis of the deviation of the supply flow rate obtained by the supply flow rate deviation obtaining means (step 406).