PURPOSE: To sufficiently reduce a wind resistance on a rotor by a strong wind and thus prevent damage on the rotor, by providing rotor which is freely foldable in the direction of a rotary shaft with the help of a link mechanism.

CONSTITUTION: A pin 13 axially attaching a rotor 4 in a radially moving way is provided on a rotary shaft 12 upheld on a body 1 in a freely moving manner. Also it is arranged so that the rotor 4 may be foldable in the direction of the rotary shaft 12 with the assistance of a piston 14 which slides a cylinder inside the rotary shaft 12 axially and a link which connects the end of the piston 14 and the rotor 4. The aforementioned rotor 4 is folded by pushing the piston 14 to the right through supplying of a fluid from a feeder ring 17, discharging fluid inside the right chamber of the piston from the feeder ring 16, pulling the rotor 4 with the piston 14 via the ring 15 and finally in such manner that the folding is effected as if getting remote from the shaft. Thus it is possible to minimize an outer force on windmill and protect the rotor 4 during a strong wind.