To alleviate a load applied to a main shaft mast by controlling the length and the wind hitting angle of a rotor blade according to the strength of the wind and remarkably increasing a start range of a wind power generation facility, and controlling the length of the rotor blade with an auxiliary blade during strong winds.

By mounting the auxiliary blade 5 on the rotor blade of the wind power generation facility, the auxiliary blade 5 is used for preventing deflection and twisting of the rotor blade, and a wind hitting length angle of the rotor blade is controlled to be changed to match the strength of the wind. Thereby, the power generating width is increased, and the load on the main shaft mast can be alleviated.

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