PURPOSE: To correctly place a core material on a fixed position on the inside of a cavity, by a method wherein a pocket part receiving hinge metal fitting stuck firmly to a base end part of the core under a state wherein the core material is inserted into the cavity is provided in a mold, through which a stationarily device, which is fitted in incapably of making a movement of an axial direction of the core material, is constituted.

CONSTITUTION: A long and slender form cavity 10 corresponding to an external form of a wearing part on an ear and a crust is formed on a bottom force 9a of a mold 9. A pocket part 12 for receiving hinge metal fittings 6 of a core material 3 is formed on a base end part of a longitudinal direction of cavities 10 each. When the core material 3 of a bow is inserted into the cavity 10 under a state where the top and bottom forces of the mold 9 are released, a holding pipe 16 is shunted from the inside of the cavity 10 with double action of a cylinder 21. At the time of insertion of the core material 3, the hinge metal fittings 6 are inserted into the pocket part 12 by putting the hinge metal fittings together with the holding pipe 16. With this construction, the core material 3 can be situated at the center of the cavity 10.