To provide an excellent output controllability excellent in maintainability and low in cost.

A plurality of blades 15 are fixed to the hub 16 of the main shaft of a generator. Each of the blades 15 comprises a blade body 15a having an aerodynamic center Xa extending linearly in a rotating radial direction and a backward blade part 15b having an aerodynamic center Xb extending from the tip part of the blade body 15a to the rear side in a rotating direction. By producing a torsional force in the blade body 15a by a pressing force Fo produced on the backward blade part 15b by wind in a rotating axis direction, a pitch angle α can be adjusted.