To realize reduction of the entire weight and to reduce the manufacturing cost by automatically controlling a pitch angle of a blade 15 via a simple and inexpensive mechanism and reducing bending load applied to the blade 15.

A base end of the blade 15 is separated from an outer peripheral face of a rotary shaft part 14, and the base end and the rotary shaft part 14 are connected by an elastic support member 17 that supports the base end and the rotary shaft part 14 in a twisted state. When centrifugal force is applied to the blade 15, twisting of the elastic support member 17 acts to increase the pitch angle of the blade 15 by rotating the blade 15 with the twisting center as an axis of the pitch angle upon the twisting of the elastic support member 17 being released so that the elastic support member 17 is elastically deformed to allow outward displacement of the blade 15. Further, a support shaft 19 projected forward to extend from the rotary shaft part 14 is provided, and the support shaft 19 and the blade 15 are connected by a wire 20.

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