PURPOSE: To provide a gas system fire extinguisher excellent in safety without a personal accident due to erroneous emission by providing a change-over means in a gas flow path to emit fire extinguishing gas according to a normal starting signal and prevent the fire extinguishing gas from emission according to an abnormality detecting signal.

CONSTITUTION: A gas system fire extinguisher 1 is provided with a controlling means 7, normal starting means 10 connected to the controlling means 7 and consisting of a sensor group 8 and starting box 9, abnormality detecting means 11 for sending various abnormality detecting signals to the controlling means 7, indicating section 12 and switch group 13. In the occurrence of a fire, a normal starting signal is outputted from the normal starting means 10 to a judgment controlling means 7 and a starting gas emitting signal is outputted to a starting gas emitting means 4 which emits starting gas through a change-over means 5 to a fire extinguishing gas emitting section 15 from which fire extinguishing gas is emitted to a protective area. When the abnormality detecting means 11 detects abnormalities such as the presence of persons in the protective area, the abnormality detecting signal is outputted to the controlling means 7 which outputs an operation inhibiting signal to the emitting means 4 and a drive means 6 and the change-over means 5 changes over a gas flow path from the emitting means 4 to the atmosphere side.