Abstract: A fuel-cell device according to this invention comprises switching valves which open at the time of the urgent stop of the device or the suspension of electric power and which are arranged outside a cell vessel, first and second differential pressure detectors which detect the differential pressures of an excess fuel pressure and an excess air pressure with respect to a nitrogen pressure in the cell vessel respectively, and first and second pressure controllers which control the opening and closing operations of a fuel differential pressure control valve and an air differential pressure control valve in response to the outputs of the first and second differential pressure detectors respectively.