PURPOSE: To surely enable setting at high accuracy even if a core has complicate shape and heavy wt. by setting the core to resin mold transferring surface shape of a master pattern and using a mold retransferring shape to parting plane of the master pattern.

CONSTITUTION: The resin mold 9 formed with a master pattern (the following shows as front pattern) for forming cavity on the front of the mold can transfer the front pattern. Therefore, at the time of setting the core 3 on this mold 9, this precisely positioned to form the space having the same shape as a product. Successively, by pouring and curing molten resin in this space 8a, this resin is integrally fused with the resin mold 9 before-hand formed. By this method, at the time of removing the core, a core mark, which the core can be surely held in high precision at the time of molding work, is obtd. Then, parting agent for resin is coated on the core and removal of this form the resin after curing can be facilitated.