A fuel cell system includes a first heating mechanism and a second heating mechanism. The first heating mechanism supplies a reformer with some of an exhaust gas discharged from a fuel cell stack as a heat source for directly heating the reformer. The second heating mechanism supplies the remaining exhaust gas to the heat exchanger and utilizes the heat generated in the heat exchanger as a heat source for indirectly heating the reformer. Temperature sensors are attached to the reformer. An open/close valve is adjusted based on the temperatures detected by the temperature sensors to control the ratio between the amount of heat supplied from the first heating mechanism to the reformer and the amount of heat supplied from the second heating mechanism to the reformer.