PURPOSE: To obtain a molded product as a unit without division of an outer shell receptacle, by a method wherein a product in a blow-molded product is covered with a low-fusing alloy to form a core in an appropriate shape, and after a molded product is obtained using a core, the low-melting alloy is molten for removal.

CONSTITUTION: A part 1, housed in a blow-molded product, is housed in a core- forming mold 3, a low-melting alloy (50% Pb, 50% Sn, a melting temperature of 200°C) is cast in a gap between the mold 3 and the part 1 to form a core in a given shape in which the part 1 is casted by opening the mold 3. The core is then placed in a mold heated to 160W180°C, a glass base material-filled phenol resin is injected into the mold 4 through an injection molder 6 to obtain a molded product 5 in a given shape. The molded product with a part, where the core is partially projected, with its face down is placed in a furnace 7 of 220W230°C and heated for about 30min to melt out the low-melting alloy.