A shutoff value provided on the entrance side and exit side of a fuel cell system has a diaphragm. A valve closing-side pressure chamber is provided on the upper face side of the diaphragm, and a valve opening-side pressure chamber is provided on the lower face side of the diaphragm. With the valve closing-side pressure chamber of the shutoff valve pressurized, the pressure in the chamber is maintained by ViS, Vic, and ViO in an electrically non-conducted state. Also, the pressure in the valve opening-side pressure chamber of the shutoff valve is maintained released. By this, force acting in the direction of closing a valving element acts on it through the diaphragm, maintaining the shutoff valve closed.