Gas turbine plant and method of cooling gas turbine plant

A gas turbine plant and a method of cooling a gas turbine plant, which can suppress condensation of moisture and can ensure high reliability. A plurality of stator blades (61a,62a,63a,64a) having cooling channels formed therein to allow passage of a coolant are arranged in a turbine, and coolant channels are arranged to introduce humid air produced by a humidifier (1,4) to inlets of the cooling channels in the stator blades. The coolant is supplied under condition to suppress condensation of moisture in the coolant supplied to at least one of the coolant channels.