Abstract: A combined cycle power plant is provided that carries out mixing of steams heated to a high temperature by cooling a high temperature cooled part of a gas turbine. Other steam favorably, guarantees the safety of the alternating current apparatus, so that it is operated stably over a long period of time. The combined cycle power plant is equipped with a mixing tube that mixes exit steam from a steam cooling system and a bypass steam. The exit steam from the steam cooling system that has been heated by cooling the high temperature cooled part of this gas turbine and the bypass steam that is not introduced into, but bypasses, this high temperature cooled part in order to control flow volume and temperature of the steam introduced into the high temperature cooled part are introduced into the mixing tube and mixed. Thus a mixed superheated steam having uniform pressure and temperature is formed, and there is no deleterious effect on any downstream equipment.