In a fuel cell system which controls an operation of a converter on the basis of a duty command value including a feedforward term, the deterioration of a response of the converter at a time of a rapid increase (a rapid decrease) of a load is suppressed. There is disclosed a fuel cell system comprising a converter disposed between a fuel cell and a load device, and a controller for controlling the operation of the converter on the basis of the duty command value including the feedforward term, wherein the controller calculates the feedforward term by use of a command value of a physical amount concerning the converter in an operation range where a requested power from the load device is in excess of a predetermined threshold value.