To permit fire extinguishing without involving chemical toxicity and reducing the ozone depletion coefficient and global warming coefficient to zero by using an O-group inactive gas such as an argon or a gas of a mixture of the argon and nitrogen, or the like, for a fire extinguisher used for a fire of a metal such as magnesium, aluminum, titanium, or the like.

When extinguishing a magnesium fire that may occur in the processing of magnesium with a machine tool such as a machining center, an O-group inactive gas such as argon or the like or a gas as a mixture of the argon and nitrogen, or the like, is used to constitute metal fire extinguisher. The O-group inactive gas includes argon, helium, neon, or the like. The gas as the mixture of such O-group gas and nitrogen, or the like, includes a gas called IG-55. In a machining center, if a fire occurs, a fire detection sensor 1 reacts, opening the valve opening device of a fire extinguisher vessel 2, thereby ejecting an inactive gas in a fire extinguisher vessel 2 from a fire extinguishing nozzle 3 for fire extinguishment.