A fuel cell system includes a desulfurizer that removes a sulfur compound in a raw material, a fuel cell unit that performs electric-power generation using fuel obtained by reforming a raw material from which the sulfur compound is removed and electric-power generation air supplied, a combustion exhaust gas passage through which combustion exhaust gas generated by combusting fuel not utilized for the electric-power generation in the fuel cell unit is emitted, a combustion exhaust gas container that is connected to the combustion exhaust gas passage and accommodates the desulfurizer inside the combustion exhaust gas container, a purifier that removes carbon monoxide included in the combustion exhaust gas, and an air heat exchanger that performs heat exchange of the combustion exhaust gas and the electric-power generation air supplied to the fuel cell unit.