The present invention provides a fuel cell system using combustion heat for an evaporator and a desulfurizer effectively. The fuel cell system comprises a combustor, a reformer, a fuel cell, a first cathode air heating part, a desulfurizer and an evaporator. A mixture of oxygen and gas which is contained in fuel is combusted in the combustor. A combustion exhaust gas generated in the combustor flows in the fuel cell system in such a manner that the combustion exhaust gas gives thermal energy to the reformer, the first cathode air heating part, the desulfurizer, and the evaporator in this order.