A blade-root-forming piece (10) is provided with: embedded metal (12), on which a nut (12A) having a hole in which an internal thread (13) has been cut, and a protrusion (12B) that protrudes in the circumferential direction of a blade root from the nut (12A), are disposed; a core material (14), which is disposed adjacent to the protrusion (12B) on the blade apex side of a wind turbine blade; and an FRP-wound layer (16), which is layered by winding a unidirectional fiber prepreg around the protrusion (12B) and core material (14), and is formed by hardening the unidirectional fiber prepreg.
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