To perform automatic control of regulation of the rotation speed of a wind mill by a method wherein a wind pressure is regulated according to a change in a wind velocity.

Blades 13 are arranged at the outer periphery of a shaft 11, and the outer end part of the blade 13 is supported on the rotary shaft 23 of a support member 15. One end of a coupling member 17 is coupled to the inner end part of the blade 13 and the other end of the coupling member is coupled to a distance regulation member 30 mounted on the shaft 11. One end side of the resilient member 40 is locked at the distance regulation member 30 and under the presence of the resilient member 40, the distance regulation member is rotated around the shaft 11 as rotation resistance is exerted thereon. When a wind pressure exerted on the blade 13 is increased, the distance regulation member 30 is rotated in a direction opposite to the elasticity exerting direction of an elastic member, and a distance between the shaft 11 and the inner end part of the blade 13 is changed to regulate a wind pressure area.