A gas turbine installation is provided in which turbine cooling air can be humidified with water while suppressing deterioration of the reliability of turbine blades. The gas turbine installation comprises a compressor for compressing air, a combustor for burning compressed air and fuel, a turbine driven by combustion gas, and a humidifier for humidifying the compressed air extracted from an intermediate stage or a discharge section of the compressor. The compressed air humidified by the humidifier is used as turbine cooling air. The humidifier includes a water distributor for adjusting an amount of water added to the compressed air.