PURPOSE: To provide a compact apparatus for utilizing a wind force by providing a main valve of pilot pressure drive system to control the pilot pressure in accordance with temperature of a main circuit when the liquid discharged from a hydraulic pump driven by a wind mill is utilized for operating a heating system or the like.

CONSTITUTION: A wind mill 1 rotated by wind force drives a hydraulic pump 2 to conduct working liquid A discharged from said pump to a heat exchanger 5 for exchanging heat with water B in a water supply circuit 10 after heating said liquid in an orifice 4 as an exothermic means in a main circuit 3. Then, the working liquid A is returned to the suction side of the pump 2 through a jet booster 6. In said apparatus, a main valve 7 controllably opened and closed by pilot pressure from a pilot circuit 8 is interposed in the main circuit 3, and a sub-valve 9 interposed in a working liquid flowing line 8a of the pilot circuit 8. Also, is provided a temperature sensing actuator 11 which controllably opens and closes the sub-valve 9 so that the temperature of the main circuit 3 does not exceed a set value.