Gas turbine and operation method of gas turbine

A gas turbine having a compressor for compressing air, a combustor (2) for taking in compressed air discharged from the compressor (1), mixing it with fuel, and burning them, and a turbine (3) driven by combustion gas generated in the combustor (2), comprising: inlet guide vanes (6) installed at a stage near an inlet of the compressor (1) for adjusting a compressor flow rate by changing an attaching angle thereof, a steam injection mechanism (7) for injecting steam to the combustor (2), a steam adjustment valve for adjusting the steam injection rate, and a steam rate control mechanism for adjusting an opening of the steam adjustment valve, a steam monitoring mechanism (23) for monitoring the steam rate injected to the combustor (2), an air temperature monitoring mechanism (24) for monitoring an atmospheric temperature, and a control unit (46) for determining whether a restriction value of the steam injection rate using a temperature, an opening of the inlet guide vanes (6), and the steam injection rate as indexes is satisfied, and controlling at least one of a temperature of air flowing into the compressor (1), the steam injection rate, and the inlet guide vane opening.