The present invention provides a humid air turbine having a compressor, a humidificator for generating humid air by adding moisture to compressed air supplied from the compressor, a combustor, a turbine, a recuperator for effecting heat exchange between exhaust from the turbine and the humid air, an economizer for effecting heat exchange between exhaust from the recuperator and water, and a system for supplying the water heated by the economizer to the humidificator. The humid air turbine includes a temperature measurement device for measuring the temperature of gas discharged from the economizer, and a control device for adjusting the amount of moisture to be supplied to the humidificator in accordance with a temperature signal from the temperature measurement device. The present invention assures low NOx of combustor and flame stability before and after water addition to the humid air turbine.