PURPOSE: To reduce the mixed quantity of oxide into the inner part of a product at the time of casting at high pressure by arranging an almost elliptic-shaped molten metal buffering plate so as to be vertically movable in a vertical type injection sleeve.

CONSTITUTION: At the time of starting the pouring of molten metal onto the molten metal buffering plate 62 having a little head drop of the molten metal after sucking up the molten metal from a molten metal holding furnace, the molten metal is flowed down on the inner wall surface of the injection sleeve 24 from a gap 69 and stored in the injection sleeve 24 while replacing with the air. Successively, at the time of pouring the molten metal into the injection sleeve 24 through the gap 69b, the molten metal surface is gradually ascended and the remained air in the sleeve 24 is discharged from the gap 69a. Just before completing the pouring of molten metal into the injection sleeve 24, the ascent of the molten metal buffering plate 62 is stopped and the molten metal surface is positioned to a little upper part from the upper surface of the molten metal buffering plate 62. At the time of completing the pouring of molten metal, a ladle executes the dip-up of the molten metal in the molten metal holding furnace. The oxide floated up on the molten metal surface is stuck to the upper surface of the molten metal buffering plate 62 and the molten metal buffering plate is retreated to a suitable position as it is.