A fuel cell system of the present invention includes a fuel cell stack, a fuel feeder that provides the fuel cell stack with fuel, a fuel cell DC/DC converter that converts the output voltage of the fuel cell stack to a predetermined voltage and then outputs it, a rechargeable battery that is an electric storage device, and a rechargeable battery DC/DC converter that converts the output voltage of the rechargeable battery to a predetermined voltage and then outputs it. The setting of a voltage at a node at which an output end of the fuel cell DC/DC converter and an output end of the rechargeable battery DC/DC converter are connected together is changeable, and the rechargeable battery is detachable. As a result, the fuel cell system of the present invention has high versatility.