PURPOSE: To achieve saving of energy in a wind power generating system, by detecting wind pressures on the windward and leeward sides, and controlling the direction of a propeller turning shaft, the pitch angle of the propeller and the direction of air flow by means of a computor.

CONSTITUTION: A positive pressure and a negative pressure are detected by a wind pressure detector, and a computor 5 determines the direction of air flow capable of obtaining the greatest pressure difference. The computor 5 opens a control valve 3 in an air passage 2 while closing other valves and controls a propeller turning shaft of a propeller type wind turbine power generating apparatus 6 to direct the same in an optimal direction. Further, since the computor determines and controls the optimal pitch angle of the propeller through calculation of the incident velocity of wind to the propeller from the value of pressure difference, it is enabled to achieve saving of energy in the entire system.