To provide a wind power generation device increasing degree of freedom in installation of a wind mill, not requiring to excessively increasing strength of a tower or a tower installation part when a windmill is installed on the tower, facilitating work at a time of attachment adjustment and maintenance of a generator, and capable of keeping output of a generator not changing excessively even at a time of change of windmill rotation due to change of wind quantity.

Air compressors 4 are connected to a plurality of rotary shafts 2 of horizontal shaft windmills 1 provided on a top part of a plurality of windmill support tower 3 respectively. The air compressors and a compressed air storage tank 7 are connected by air piping and air compressed by the air compressor is stored in the air tank. The air tank, an air motor 9 and the generator 10 are installed near a root part of the tower. The air motor is rotated by compressed air in the air tank and generates power by a generator.