PURPOSE: To prevent breakdown of blade fixing section while to prevent noise by fixing a blade having streamlined circumferential side rotatably at the portion of support facing with the blade of wind force turbine.

CONSTITUTION: A blade 10 having streamlined circumferential side is fixed rotatably through ball bearings 11 at upper and lower ends to the portion of support 1 facing with the blade 3a of wind force turbine 3. Consequently the blade 10 will rotate such that the pointed end (P) will always direct downstream thereby wind blowing to collide against the support 1 as shown by arrow W2 will flow smoothly along the blade 10 to prevent production of eddy and dropping of wind speed at the downstream of support 1, resulting in prevention of breakdown of fixing section due to rolling of blade 3a and production of noise due to vibration of blade 3a.