To efficiently suppress a reduction in material rigidity of an embedding part for a high-pressure, front stage rotor blade of a steam turbine by automatically calculating the optimal temperature and flow of cooling steam according to the operating conditions of the steam turbine to control its temperature and flow to their optimum values and then applying them to the high-pressure, front stage rotor blade embedded part.

In controlling cooling steam for cooling an embedding part for a high-pressure, front stage rotor blade of a high-pressure turbine, a temperature sensor 38 and a pressure sensor 37 detect the temperature and pressure of a high-pressure, front stage rotor blade outlet respectively and a computing element 39 calculates the proper temperature and flow of cooling steam. Signals from the computing element 39 open or close flow regulating valves 35a to 35c to control the temperature of a cooling steam header 34 to its proper temperature. A temperature sensor 36 detects the temperature of the cooling steam header 34 and then feeds back it to the calculating element 39 which in turn opens the regulating valve on the low-temperature side as well as closes the regulating valve on the high-temperature side when the fed-back temperature is higher than the optimal temperature and vice versa when lower than the optimal temperature.