A fuel cell system (1) includes a desulfurizer (11) that removes a sulfur compound in a raw material, a fuel cell unit (50) 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 (50) is emitted, a combustion exhaust gas container (10) that is connected to the combustion exhaust gas passage and accommodates the desulfurizer (11) inside the combustion exhaust gas container (10), a purifier (12) that removes carbon monoxide included in the combustion exhaust gas, and an air heat exchanger (13) that performs heat exchange of the combustion exhaust gas and the electric-power generation air supplied to the fuel cell unit (50).