The cooling capacity of a first heat exchanger for cooling a reformed gas introduced into an inlet of a circulation pump is increased as an output of a fuel cell increases. With this configuration, an inlet temperature of the circulation pump is relatively high during low power generation and decreases as the generation power increases, and a volumetric flow rate during high power generation in which a large amount of reformed gas is required can be decreased relatively. As the result, a dynamic range required for the circulation pump can be made small. Furthermore, water condensation in the inlet of the circulation pump can be prevented during low power generation.