PURPOSE: To obtain the titled item that has little residual stress and no void with the cooling period for the item shortened, by drilling a plurality insertion bores horizontally in a movable mold, and inserting slidably a plurality of cooling rods supported by a plunger into said insertion bores.

CONSTITUTION: For example, with the cooling rods 16 sufficiently inserted into the horizontally formed insertion bores in the movable mold 12, a valve 20 is opened to evacuate the mold, and then a heated and melted plastic is injected via an injection pipe 22. Then after the valve 20 is closed, the plunger 18 supporting the cooling rods 16 is finely vibrated so that the cooling rods 16 are vibrated to the right and left to perform cooling. Then after the mold and the cooling rods are cooled to a prescribed temperature, the cooling rods 16 are withdrawn with them being vibrated horizontally under such a condition that the resin is under pressure by opening the valve 20, so that the temperature distribution of the resin in the mold is kept constant while it is being cooled. After the movement of the cooling rods 16 is stopped, the intended item is obtained by mold-releasing.