A fuel cell system and method comprising a fuel cell stack formed by stacking fuel cells, a high voltage energy storage capable of being directly coupled to the fuel cell stack, a DC-DC converter connected to the fuel cell stack and the energy storage, a load operated by consuming at least electrical energy generated by the fuel cell stack or electrical energy discharged from the energy storage, a fuel cell warming up control unit for warming up the fuel cell stack, and a voltage adjustment unit for implementing voltage control to control the output voltage of the fuel cell stack to become equal to, or higher than the terminal voltage of the energy storage, at the time of warming up the fuel cell stack.