A manufacturing method comprising: a process S1 of forming a plate member which has a substantially annular scrap portion having a center hole through an axial direction and a core plate portion defining a portion of the core pieces arranged continuously with the scrap portion on a radially inner side of the scrap portion; a process S2 of forming a laminated body, which has the core pieces, by laminating the plate member; a process S3 of providing the laminated body and the shaft in a mold; a process S4 of forming a molding body by inserting a molten resin or a nonmagnetic material in the mold and forming the filling portion of which at least a portion is located between the core pieces; and a process S5 of separating the scrap portion and the core plate portion.