Abstract: A gas turbine comprises a compressor for compressing a gas supplied therein and discharging the compressed gas, a combustor in which the discharged gas from the compressor and a fuel are combusted, a turbine to be driven by a combustion gas from the combustor, and an injection unit which injects water into the gas to be supplied to the compressor, thereby lowering the temperature of the gas to be introduced into the compressor than the atmospheric temperature, and causing water droplets having been injected in the gas and within the compressor to be vaporized while flowing down therein, wherein the quantity of water spray injection is controlled while monitoring operational conditions of the gas turbine.