FUEL CELL SYSTEM

Provided is a fuel cell system for generating electricity by supplying a fuel cell with an anode gas and a cathode gas, the fuel cell system including: a buffer tank for storing an anode-off gas discharged from the fuel cell; a control valve for controlling a pressure of the anode gas supplied to the fuel cell; and anode gas pressure control means for controlling the control valve to increase the pressure of the anode gas as a required output increases. The anode gas pressure control means adjusts, in a transient operation in which the required output decreases, an opening of the control valve to a predetermined opening, thereby decreasing the pressure of the anode gas while supplying the anode gas.