The present invention enables the determination of an operating point of a fuel cell so as to prioritize the fulfillment of an amount of required power generation while avoiding various limitations, such as a current limit, in a fuel cell system that warms up the fuel cell by a low efficiency operation.A controller 70 multiplies a voltage command value Vcom obtained in step S3 by a current command value Icom obtained in step S1, then, this is divided by a final voltage command value Vfcom obtained in step S4, thereby obtaining a final current command value Ifcom to determine an operating point (Ifcom, Vfcom) during a warm-up operation (step S5), and then the process ends.