To improve fire extinguishing efficiency by the radiation of water fine spraying executed following the discharge of a nitrogen gas, and to secure safety even when an oxygen concentration is fully lowered by the nitrogen gas discharge.

In a protective space 10 within a sealed section, a gas nozzle 12 for discharging the nitrogen gas and a fine spraying nozzle 14 for mixing and discharging the water fine spraying of a particle size 10 to 200 μm and the nitrogen gas are provided. A control board 24 discharges the nitrogen gas from the gas nozzle 12 to lower the oxygen concentration inside the protective section 10 first, then stops the discharge from the gas nozzle, mixes the nitrogen gas from the fine spraying nozzle 14 and discharges the water fine spraying.