hand it can be considered that the steam on the outlet side of the high pressure turbine 4 is made use of so as to cool the turbine rotor 28 in view of the steam process regarding the combined cycle power generating device thereby the temperature of the steam on the outlet side of the high pressure turbine 4 is lower than the temperature of the transition piece cooling steam however the temperature of the steam on the outlet side of the high pressure turbine 4 is excessively lower than the temperature of the transition piece cooling steam and the cooling effect is surplus hence when the steam on the outlet side of the high pressure turbine is used for cooling the turbine rotor 28 and the intermediate pressure turbine 2 the temperature control becomes difficult therefore it is preferable to use the steam of which the temperature is higher than the temperature of the steam on the outlet side of the high pressure turbine 4 and lower than the temperature of the steam streaming through the flow line marked with the symbol b in fig2 and the transition piece cooling steam satisfies this preferable condition and is optimal as the cooling steam that cools the part in question further toward the location between the stator blades 24 a of the first stator cascade in the intermediate pressure turbine 2 and the rotor blades 26 a of the first rotor cascade in the intermediate pressure turbine.