PURPOSE: To prevent involution of oxide in molten metal into cavity in a mold by making the same height of the molten metal surface in a stoke before and after casting as the upper face of a filter fitted at higher position than the molten metal surface in a holding furnace at mold sprue side in inner part of the stoke.

CONSTITUTION: At the time of returning back the molten metal in the stoke 20 into the holding furnace 24 after completing casting, even if the molten metal surface in the holding furnace 24 varies, the pressures at the holding furnace side and the metallic mold side are controlled with a computer so that the molten metal surface height in the stoke 20 before and after casting comes to almost the same height as the upper face of the filter (b). The oxide in the molten metal in the holding furnace 24 is mainly filtered with the filter (a) and the oxide of the molten metal which is ascended to the sprue part of the cavity in the metallic mold at the time of casting and returned back to the stoke while sticking to the inner wall of the stoke after completing the casting is mainly filtered with the filter (b) to prevent the involution of the oxide into the cavity in the metallic mold.