PURPOSE: To provide a small sized gas turbine capable of operating an air compressor part from a partial load to its full load with the highest efficiency and making anti-surge control.

CONSTITUTION: In a gas turbine provided with a first air compressor 1, having no self discharge pressure control function, a combustor 2, and a turbine 3, a second air compressor 4 is arranged independently. A communicating pipe 5 is provided so as to supply high pressure air discharged from the second air compressor 4 to the outlet of the first air compressor 1 or the inlet of the turbine 3. A pressure control valve 6 for controlling pressure of high pressure air is provided in the communicating pipe 5. The second air compressor 4 can be arranged coaxially with the gas turbine through a decelerator.