PURPOSE: To operate a wind mill efficiently by fitting variable blades on main body supports to be movable, jointly providing edges of variable blades with auxiliary blades, and together providing variable and auxiliary blades with control rods and joint rods for elevation positioning.

CONSTITUTION: Variable blades 3 are fitted on main body supports 1 of a wind mill via support shafts 2 to be movable. Auxiliary blades 4 are jointly provided to edges of variable wings 3 with hinges 5 between. Variable blades 3 and auxiliary blades 4 are together provided with control rods 6 and joint rods 7 for elevation positioning. This construction permits to change elevations of blades face in accordance with the change of wind direction for operating the wind mill efficiently.