PURPOSE: To reduce the time for dissolution and to improve dimensional accuracy and the yield of production by inserting a supporting bar provided with a through-hole into a ceramic core and eluting the core by the dissolving liquid fed through the through-hole.

CONSTITUTION: A supporting bar having a through-hole through which a dissolving liquid to dissolve a ceramic core can flow is prepd. The ceramic core is molded after the supporting bar is contained into the ceramic core so that the deformation of the core is suppressed by the supporting bar. Such core is set in a casting mold and the outside of the core is embedded by a molten metal which is then cooled to solidify. Such casting is dippied into a dissolving liquid for the ceramic core to permit easy infiltration of the dissolving liquid into said through-hole thus eluting easily the ceramic core.