PURPOSE: To enable setting of the thermal energy of air freely at high temperature while to facilitate handling of the working fluid by arranging a pressure or flow regulation valve at the delivery side of an air compressor to be driven through rotation of windmill.

CONSTITUTION: Upon rotation of a windmill 1, an air compressor 2 will rotate to deliver the air through a delivery port 4. When closing a pressure regulation valve 8 gradually, the pressure of air flowing through an air tube 3a, a heatexchanger 5 and an air tube 3b will increase thus to increase the temperature. Here, the thermal energy of air is collected through the heatexchanger 5. Since the temperature of air is determined on the basis of the pressure level, the temperature can be set by regulating the opening of the pressure regulation valve 8 if the necessary air temperature is previously determined. Consequently, the temperature of heat can be set freely at high level while handling of the working fluid is facilitated.