PURPOSE: To provide ease of inner mold removal without damaging a molded coil by placing a high molecular material, which has a thermal expansion coefficient difference between itself and a mold resin situated within a certain range, between a mold of square tube plate vessel contour constituting an inner mold and placed at the center and a mold of tube plate vessel contour placed on the former's circumference.

CONSTITUTION: This manufacturing mold consists of a mold 1 of square tube plate vessel contour, a high molecular material board 2 placed around the mold 1 and a mold 3 of tube plate vessel contour situated on the circumference of the material board 2, and with its one surface governing the inner dimensions of a molded coil and the other surface facing the material board 2. One of said molds 3 of tube plate contour having an arc or square surface is fitted with an inner bottom plating 4 having the same shape and dimensions as that of an auter mold bottom face. Placed on this plaqing 4 are the mold 1, the high molecular material boards 2 and the mold 3, forming a body of an inner mold. A high molecular material used for said high molecular material boards 2 must have a larger thermal expansion coefficient than that of a mold resin and a coefficient difference between them fallen within a range of 10×10-6W 50×10-6/°C.