A temperature adjustment member is arranged to control temperature of a reformer independently of temperature of a fuel cell module. The reformer is structured as a three-fluid heat exchanger into which a fluid is introducible whose temperature is higher or lower than exhaust-gas temperature of the fuel cell module. Then, the temperature of the reformer is controlled independently of operation temperature of the fuel cell by introducing the higher-temperature or lower-temperature fluid into the reformer. Also, a high-temperature or low-temperature gas is mixed with the module's exhaust gas, thereby adjusting temperature of the exhaust gas itself. This also controls the temperature of the reformer independently of the operation temperature of the fuel cell.