To provide a gas turbine plant, capable of efficiently recovering heat from exhaust gas of a gas turbine and capable of improving efficiency of a plant by a simple and small-sized facility, without providing a large-sized regenerative heat exchanger.

In a gas turbine plant, air or a gas A0 taking air as a main component is compressed in a compressor 1, the compressed gas is used for a gaseous combustion improver for a gas turbine, a gaseous operating medium or a gaseous cooling medium. A gas A, compressed in the compressor 1, is made into a high-temperature compressed gas A1 through heat recovery to exhaust gas of the gas turbine, saturated steam or superheated steam obtained by heat exchange in gas turbine exhaust gas is mixed to the high-temperature compression gas A1 into a humidified gas B, and the high-temperature and high-pressure humidified gas B is used for a gaseous combustion improver, a gaseous operating medium or a gaseous cooling medium for the gas turbine.