PURPOSE: To make a structure extremely simple and to prevent explosion and combustion by mounting a hydrogen gas discharge valve a hydrogen exhaust header and an inert gas discharge flare for spraying inert gas to the hydrogen exhaust header.

CONSTITUTION: When an inert gas discharge valve 3 is opened to discharge nitrogen gas, the air in a hydrogen exhaust header 1 and the periphery thereof is excluded to form a nitrogen atmosphere. Subsequently, when a hydrogen gas discharge valve 2 is opened to discharge hydrogen gas, the hydrogen gas successively passes through a hydrogen gas lead-out pipe 5 and the valve 2 to enter the hydrogen exhaust header 1. At this time, since the interior of the header 1 is under the nitrogen atmosphere, there is no possibility of explosion and combustion and, further, since the hydrogen exhaust header 1 is fanwise, the speed of the hydrogen gas is decelerated the moment said gas enters the header 1 and the possibility of ignition due to friction or static electricity is lowered. A discharge area is enlarged and the discharge speed of the hydrogen gas is made slow to diffuse the hydrogen gas into the atmosphere by the blow of nitrogen gas.