The present invention provides a gas turbine and a method of operating a gas turbine capable of suppressing a decrease in reliability of the compressor due to steam injection quantity, temperature change (the compressor suction temperature), the degree of opening of the inlet guide vane brought. Feature of the present invention is a control means, the control means in order to meet the temperature, the degree of opening of the inlet guide vane and the steam injection quantity as the injection quantity of steam index limit values, control the air flowing into the compressor the temperature of the steam injection amount or the degree of opening of the inlet guide blade at least one. Further, in the gas turbine, instead of having a monitoring means monitoring the pressure of steam injection amount ratio is set in advance for each atmospheric temperature conditions, pressure ratio and inlet opening wing guide wings for causing the load or no surge margin amount exceeds a predetermined limit value, it is possible to limit or control the degree of opening of the inlet guide wing or steam injection amount.