To provide a wind power generation device that can improve generating efficiency by reducing a wind velocity capable of starting a windmill via a relatively simple structure.

A frame 15a of a generating set 15 houses a main generator 16 and an auxiliary generator 17, and the main generator 16 has an extended rotor shaft 18. A disklike main hub 20 mounted with three platelike blades 21 is integrally rotatable mounted on a tip portion of the rotor shaft 18 passed through a cylindrical part 19 fixed to the outside of the frame 15a to constitute a part of the frame 15a, to constitute a main windmill 22. An auxiliary hub 27 mounted with two blades 28 having the same size and shape as the blades 21 is integrally rotatably mounted on an outer ring part 26a of a radial bearing 26 fixed on the circumference of the cylindrical part 19, to constitute an auxiliary windmill 29. The auxiliary windmill 29 is arranged in such proximity to the main windmill 22 as precludes contact, and is designed to rotate in the opposite direction to the main windmill 22.