It is possible to prevent excessive power generation of a fuel cell when a failure has occurred. When a start signal is input, a fuel cell system sets an open end voltage of the fuel cell as an initial value of the output voltage of the fuel cell corresponding to the output current zero of the fuel cell. When the failure is detected, the fuel cell system reads out the open end voltage of the preset initial value as the output voltage corresponding to the output current zero and controls the voltage so that the output voltage of the fuel cell coincides with the open end voltage.