To provide an inert gas feeder capable of safely and surely extinguishing a fire by preventing a dangerous substance from being stored inside inert gas feed piping with the simple opening/closing operation of a valve and an inexpensive means.

In inert gas feed piping for feeding an inert gas for fire extinction from an inert gas holder into a dangerous substance facility, the inert gas feed piping to the dangerous substance facility is provided with an interruption/conduction means having both an interruption function for preventing the backflow of the dangerous substance from the dangerous substance facility to the side of piping while the dangerous substance facility is ordinarily operated or stopped (A) and a conduction function capable of feeding the inert gas in the case of introducing the inert gas from the inert gas holder to the dangerous substance facility when a fire occurs in the dangerous substance facility (B) so that the dangerous substance can not be stored inside inert gas feed piping.