PURPOSE: To obtain a high accuracy product free of flaws such as surface sink by a method wherein a small amount of melt molding material is jetted into a cavity to be attached to the entire wall surface and then, a pressure air is injected into hollows therein to solidify it under pressure.

CONSTITUTION: A smaller amount of melt molding material than the internal capacity of a cavity is jetted into the cavity in a mold 60 held at the temperature below the solidifying point of the molding material from a small-diameter jet hole so as to be attached to the entire wall surface of the cavity. A pressure air is injected from the jet hole before the molding material is solidified as a whole to solidify the all molding material with the hollow within the molding material pressurized.