NOVELTY - A fuel cell system includes a fuel cell stack (12) and a casing (16). The fuel cell stack is formed by stacking fuel cells (26). The casing is provided with an exhaust gas channel comprising a first channel for supplying exhaust gas to a reformer (22) as a heat source for reforming the mixed fuel gas, a second channel for supplying exhaust gas to a heat exchanger (18) as a heat source for heating the oxygen-containing gas, and a third channel for supplying exhaust gas to the evaporator (20) as a heat source for evaporating the water.    USE - For stationary application or mobile application e.g. vehicle.    ADVANTAGE - The fuel cell system efficiently utilizes the heat of exhaust gas discharged from a fuel cell stack, and effectively improves the heat recovery efficiency without increasing the size of the fuel cell system. It minimizes heat loss and achieves further improvement in heat recovery rate. The heat in the exhaust gas is collected as much as possible, thus it is not necessary to maintain the heat insulating performance for insulating the heat naturally radiated from the fuel cell system. Since the amount of heat insulating material used in the system is reduced, it is possible to reduce the overall size of fuel cell system.    DETAILED DESCRIPTION - A fuel cell system comprises a fuel cell stack, a heat exchanger, an evaporator, a reformer, and a casing. The fuel cell stack is formed by stacking fuel cells. Each fuel cell includes an electrolyte electrode assembly and a separator. The electrolyte electrode assembly includes an anode, a cathode, and an electrolyte. The heat exchanger heats an oxygen-containing gas to be supplied to the fuel cell stack. The evaporator produces a mixed fuel of raw fuel containing hydrocarbon and water vapor. The reformer produces reformed gas from the mixed fuel. The casing is provided with an exhaust gas channel as passage of exhaust gas discharged from the fuel cell stack after consumption in power generation reaction. The exhaust gas channel comprises first channel for supplying exhaust gas to the reformer as a heat source for reforming the mixed fuel gas, second channel for supplying exhaust gas to heat exchanger as heat source for heating the oxygen-containing gas, and a third channel for supplying exhaust gas to the evaporator as a heat source for evaporating the water.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross sectional view of main components of fluid unit of the inventive fuel cell system.    Fuel cell stack (12)    Casing (16)    Heat exchanger (18)    Evaporator (20)    Reformer (22)    Fuel cells (26)