As an activation time power generation mode of a fuel cell system, a control device executes: a first step of determining whether or not hydrogen is present in an anode gas flow path; a second step of bringing a contactor to a connected state if hydrogen is detected in the first step as being present in the anode gas flow path; a third step of supplying air to a cathode through a cathode gas flow path after the second step has been executed; and a fourth step of, if a voltage of the fuel cell stack detected by a voltage detection device reaches a predetermined voltage, connecting an electrical load to the fuel cell stack, and performing electric power generation of the fuel cell stack while maintaining the voltage at or below the predetermined voltage.