A fuel cell system comprising: a fuel cell performing a power generation by a fuel and an oxidant gas; a reforming portion generating the fuel from a source material and water to supply the fuel to the fuel cell; a combusting portion receiving a combustible gas that includes an unused fuel in the fuel not used for the power generation from the fuel cell and combusting the combustible gas by an oxidant gas to send out a combustion gas; a source material supply device supplying the source material; an oxidant gas supply device supplying the oxidant gas to the combusting portion; a source material flow sensor detecting a supply flow rate of the source material; an oxidant gas flow sensor detecting a supply flow rate of the oxidant gas; and a control unit controlling at least the oxidant gas supply device and the source material supply device, the control unit including a flame extinction determination portion determining whether or not a flame extinction occurs at the combusting portion, an acquisition portion acquiring an oxidant gas flow rate serving as a supply flow rate of the oxidant gas per unit time and a source material flow rate serving as a supply flow rate of the source material per unit time at a time when the flame extinction determination portion determines that the flame extinction occurs at the combusting portion, a correction portion ( S222, S226, S228) correcting at least one of the oxidant gas flow rate and the source material flow rate acquired by the acquisition portion based on at least one of tolerances of the source material flow sensor and the oxidant gas flow sensor, and a reignition portion controlling the oxidant gas supply device and the source material supply device to supply the oxidant gas and the source material at a corrected oxidant gas flow rate and a corrected source material flow rate corrected by the correction portion ( S222, S226, S228) to the combusting portion for reigniting the combusting portion, characterized in that the correction portion includes a first correction portion correcting the oxidant gas flow rate acquired by the acquisition portion by subtracting a flow rate corresponding to a half of the tolerance of the oxidant gas flow sensor. a fuel cell performing a power generation by a fuel and an oxidant gas; a reforming portion generating the fuel from a source material and water to supply the fuel to the fuel cell; a combusting portion receiving a combustible gas that includes an unused fuel in the fuel not used for the power generation from the fuel cell and combusting the combustible gas by an oxidant gas to send out a combustion gas; a source material supply device supplying the source material; an oxidant gas supply device supplying the oxidant gas to the combusting portion; a source material flow sensor detecting a supply flow rate of the source material; an oxidant gas flow sensor detecting a supply flow rate of the oxidant gas; and a control unit controlling at least the oxidant gas supply device and the source material supply device, the control unit including a flame extinction determination portion determining whether or not a flame extinction occurs at the combusting portion, an acquisition portion acquiring an oxidant gas flow rate serving as a supply flow rate of the oxidant gas per unit time and a source material flow rate serving as a supply flow rate of the source material per unit time at a time when the flame extinction determination portion determines that the flame extinction occurs at the combusting portion, a correction portion ( S222, S226, S228) correcting at least one of the oxidant gas flow rate and the source material flow rate acquired by the acquisition portion based on at least one of tolerances of the source material flow sensor and the oxidant gas flow sensor, and a reignition portion controlling the oxidant gas supply device and the source material supply device to supply the oxidant gas and the source material at a corrected oxidant gas flow rate and a corrected source material flow rate corrected by the correction portion ( S222, S226, S228) to the combusting portion for reigniting the combusting portion,