PURPOSE: To keep the fixed molten metal level while forming a large part of a furnace to the opening structure by fitting a discharging pipe opened at the fixed molten metal level height in a pressurizing vessel and a suction pipe having resistance larger than the fluid resistance of the discharging pipe and increasing/decreasing the pressure in the pressurizing vessel.

CONSTITUTION: In a molten metal holding chamber, the molten metal 13 is insulated to the heat and stored. In a ladle-out chamber 14, the molten metal 13 is kept to the fixed molten metal level and supplied into a casting machine from a molten metal supplying hole 15. At the time of lowering the molten metal level in the ladle-out chamber 14, the pressure in the pressurizing vessel 16 is reduced through an air pressure device 19 so as to suck the molten metal 13 into the pressurizing vessel 16 from the molten metal holding chamber 12 through the suction pipe 18. Successively, the pressure in the pressurizing vessel 16 is increased through the air pressure device 19 to discharge the molten metal 13 in the pressurizing vessel 16 into the ladle-out chamber 14 from an opening hole in the discharging pipe 17. At this time, the molten metal 13 reversely flows into the molten metal insulating chamber 12 through the suction pipe 18, too, but as the fluid resistance in the suction pipe 18 is larger than that in the discharging pipe 17, the reverse flowing quantity is little. When the molten metal level in the ladle-out chamber 14 returns back to the fixed molten metal level A, the air pressure device 19 is opened to the air atmosphere and the excess quantity is made to overflow.