PURPOSE: To evaluate a lot of kinds of steel materials efficiently in a single mold by setting respective gates and cavities telescopitically and replaceably in a mold in which two or more similar cavities are disposed and manufacturing said gates and cavities by means of steel materials different respectively.

CONSTITUTION: Mold main bodies (fixed side and movable side) are set in an injection molding machine, and then molten resin injected out of a nozzle 1 is passed through a sprue 2, a runner 3 and pin point gates A1-A4 and flowed into cavities B1-B4. When the inflow resin is cooled down, a moving mold 4 and a movable mold 5 are opened in the direction separated from a fixed mold 6 and the sprue 2 and the runner 3 are released and simultaneously the gates A1-A4 and the connecting sections of cavities B1-B4 are cut off and molded products of B1-B4 are released by an ejector pin 7. Sections for accom modating pin point gate constitutions A1-A4 of C1-C4 correspond to sections accommodating cavity constitutions B1-B4 of D1-D4 and are composed of steel materials of same kind. Said four groups of gate constituting sections and cavity constituting sections are manufactured by the steel materials of two kinds or more.