To provide a generating windmill that rotates continuously in a constant direction irrespective of wind direction by automatically changing the pitch of windmill vane surfaces according to wind direction.

A vane 1 of the windmill is mounted on a shaft 4 at a point 5. The vane 1 freely rotates on the point 5 and stops within a range of stoppers 2 and 2'. The stoppers 2 and 2' may be movable on springs 3 and 3' until brought parallel to the direction of the shaft 4. When a soft, windmill vane is employed and a swell of the soft vane of duck or the like is used to change the pitch normally or reversely, the windmill rotates in one direction.