PURPOSE: To obtain maximum output in a squirrel-cage shaped wind mill, by rotatably providing plural pairs of vanes symmetrically with respect to an axis of the wind mill between upper and lower frames and constituting a control mechanism in such a manner that a maximum amount of received wind is obtained by a wind receiving angle of each paired vane at each position with rotary motion of the wind mill.

CONSTITUTION: Plural pairs of vanesI,I' are mounted by vane shafts 16-19, 4-20... symmetrically with respect to a wind mill shaft 2 between upper and lower squirrel- cage shaped frames 17, 18, and rotatably constituted through the wind mill shaft 2 and gears 11W13, 3W6. In this constitution, the direction of the wind is detected by a wind direction detector plate 10, and a gear 11 follows the detection and is located to a prescribed position correspondingly to the direction of the wind, then each vane shaft 16-19, 4-20 is also set in accordance with the direction of the wind. As the wind mill rotates, a sloped angle of the vanesI,I'... is changed in accordance with gear ratio of gears 11, 12, 3, 5 by the reference of a relative position corresponding to said direction of the wind. In this way, received wind power is always obtained maximum, and maximum output operation can be performed.