To improve a response performance in a fuel cell system in which an on/off valve such as an injector is disposed in a fuel supply passage, by decreasing a pressure adjusting error occurring when the drive cycle of the on/off valve fluctuates. A fuel cell system comprises a fuel cell, a fuel supply passage for supplying to the fuel cell a fuel gas supplied from a fuel supply source, an on/off valve for adjusting a gas state on the upstream side of the fuel supply passage to supply the gas to the downstream side thereof, and control means for driving and controlling the on/off valve. The control means calculates a feed-forward correction flow rate based on the drive cycle of the on/off valve, corrects the command value of the gas injection flow rate of the on/off valve by use of the feed-forward correction flow rate, and drives and controls the on/off valve based on the command value.