To provide a fire extinguisher, wherein it is not necessary to install a pressure gas cylinder, while man-power for inspection is reduced and the maintenance cost is reduced.

The fire extinguisher includes an extinguisher main body 1 and an open injection head 2. Inside the extinguisher main body 1, a storage tank 4 for storing a fire extinguishing agent is provided, wherein the storage tank 4 is connected to an air compressor 5 and can be pressurized. The storage tank 4 is also connected to the open type injection head 2 through piping 6, and a pressure switch 10 is set in the middle of the piping 6. The air compressor 5 is designed so that driving and stopping are performed by on/off of the pressure switch 10, so that the pressure inside the storage tank 4 is controlled to be within a prescribed range.