A combined cycle power generating device in which the exhaust heat of the gas turbine reheats the steam discharged out of the high pressure chamber of the steam turbine so that the reheated steam is supplied to the intermediate-pressure chamber in order to increase the power output of the steam turbine, wherein the cooling steam that has cooled the gas turbine is supplied to the intermediate-pressure chamber via a cooling steam inlet different from the inlet of the reheat steam that is reheated by the exhaust heat of the gas turbine, so that the cooling steam is used for cooling purpose, the temperature of the cooling steam being higher than the temperature of the steam discharged out of the high pressure chamber.