PURPOSE: To accurately position a core and to improve workability by arranging flange parts at fitting ends of both cores for core pin side and cavity side, respectively, setting clamps at positions corresponding to each other frame, respectively, providing a guide groove for inserting the core in the outer frame and making fitting of the core easy with an auxiliary tool.

CONSTITUTION: The core pin side core 1 provides the fitting part 11, flange part 12 and ejecting mechanism part 13. In the fitting face 11, guide holes 14 to guide poles 24 arranged to the cavity side core 2 are board. In the cavity side core 2, the fitting face 21 and flange part 22 are provided and fitted to the core pin side core 1. Opening parts 31, 41 forming a core inserting hole 6 are provided with the lower side outer frame 3 and the upper side outer frame 4 and the clamps 7, 7 are arranged corresponding to flange parts 12, 22, respectively. In the outer frame 4, the guide poles 42 are arranged, and in the outer pole 3, the guide holes 32 corresponding to the guide poles 42 are bored. The flange parts 12, 22 are fitted with the clamp 7 and by fastening the fastening bolts, they are fixed. By this method, only by changing the core, various molded products can be formed.