This invention provides a fuel-cell system that has improved detection precision with respect to combustion-state problems. Said fuel-cell system (1) is provided with the following: a fuel cell (20) that takes in a hydrogen-containing fuel gas (E) and an oxygen-containing oxidant gas (A) and generates electricity; a reformer (10) that takes in and reforms a feedstock (D) to generate the fuel gas (E); an off-gas combustion unit (30) that burns an off-gas (Fe) discharged from the fuel cell (20); an exhaust-gas purification unit (40) that burns combustible substances in an exhaust gas (G) discharged from the off-gas combustion unit (30); a first temperature-detection unit (48) that detects the temperature of the exhaust-gas purification unit (40); a second temperature-detection unit (38) that detects the temperature of either the reformer (10) or the off-gas combustion unit (30); and a combustion-problem detection unit (91) that detects combustion-state problems in the off-gas combustion unit (30). The combustion-problem detection unit (91) uses the temperature detected by the first temperature-detection unit (48) and the temperature detected by the second temperature-detection unit (38) to determine whether a combustion-state problem has occurred.
