FUEL CELL SYSTEM

The fuel cell system is simplified and made more compact in addition to causing the favorable recirculation of hydrogen-containing off-gas regardless of the increase or decrease in the flow rate of hydrogen-containing gas. The fuel cell system is provided with: a cell unit (11) that generates electricity by means of separating hydrogen-containing gas and oxygen-containing gas from each other while placing in flow contact to each other; and a recirculation mechanism for recirculating to the cell unit (11) hydrogen-containing off-gas discharged from the cell unit (11). The fuel cell system has a flow rate determination unit(C1) that determines whether or not the hydrogen-containing gas fed to the cell unit (11) is less than a predetermined flow rate; and a gas feeding pressure varying mechanism (C2) that cause the pressure of the hydrogen-containing gas to vary to increase and decrease when it is determined that the hydrogen-containing gas fed to the cell unit is less than the predetermined flow quantity.