Provided is a fuel cell system to reduce the cost for producing hydrogen by storing the remaining hydrogen discharged at a stack unit and re-supplying the stored one to a stack unit if necessary. The fuel cell system comprises a stack unit(130) which is provided with a fuel electrode and an air electrode and generates electricity by the electrochemical reaction of hydrogen and oxygen; a fuel supply unit(110) which supplies hydrogen to the fuel electrode of the stack unit; an air supply unit(120) which supplies air to the air electrode of the stack unit; and a remaining gas storage unit(200) which stores the remaining hydrogen discharged from the stack unit or the fuel supply unit and re-supplies it to the stack unit or supplies it to the other system needing hydrogen.
