PURPOSE: To perform swiftly and reliably fitting and removal of a core without making use of joining metal fittings, by a method wherein a cavity and core are made fittable and removable detachably respectively to a stationary side mold body and movable side mold of a mold.

CONSTITUTION: A cavity 21 and core 22 are fitted respectively to a retainer plate 3 and movable retainer plate 4. Fitting recessed notches 11 whose top fringes are opened are formed respectively on both templates 3, 4, a receiving plunging piece 12 having half a thickness of the templates 3, 4 is provided in a rising state on both the top and bottom side corners and square plungers 14, 15 are provided in a plunged state. Plungers 17, 18 connecting with the plunging piece 16 and plungers 14, 15 are provided in a plunged state. Therefore, in a fitting part between the cavity 21 and template 3 and that between the core 22 and template 4, since movements of a clamping and breaking directions of a mold are mutually regulated, joining metal fittings become unnecessary. Then since a clearance of the other direction is absorbed by tapering processing of a guide pin 8, fitting and removing of the cavity 21 and core 22 can be performed swiftly.