PURPOSE: To obtain surely a positioning diameter with an accurate dimension, by forming a circular through hole by pulling a molding pin of a mold for preparing the circular through hole from an inclined circular hole in an upward and downward vertical directions without any undercut.

CONSTITUTION: A processing pin 3 of a mold 2 for processing a circular through hole 1 being vertical to a processed surface (a) of a product inclined to a horizontal plane is divided into two. One semicylindrical piece 3a and another semicylindrical piece 3b are fixed on an upper fixed mold 2a and a lower movable mold 2b respectively. The contacting surfaces of both semicylindrical pieces 3a and 3b are cut into a upward and downward direction for pulling. A dimension of a positioning diameter D is surely obtained at a crossing part of the surface with a rough central line b of the processing pin 3. Both semicylindrical pieces 3a and 3b of the processing pin 3 are pulled out from the inclined circular through hole 1 in the upward and downward vertical directions. Therefore, in the vertical pulling out of the mold 2, the mold can be pulled out from the circular through hole 1 being vertical to the inclined processing surface without any undercut. The positioning diameter D can be therefore surely obtained from a diameter passing through a crossing point of the central line b of the processing pin 3 and the cut line d in the vertical direction being a sliding surface.