PURPOSE: To prevent narrowing of the pipe inside of a cylinder and a communicating hole by opening a high-pressure inert gas source provided to a suction force system for a molten metal so as to branch therefrom and discharging the metallic oxide accumulating and sticking to and near the inside wall of the cylinder and the communicating hole into a melting furnace.

CONSTITUTION: A stirrer for a molten metal sucks periodically the molten metal in a metal melting furnace 1 into a cylinder 4 communicating with the furnace 4 by evacuating the cylinder 4 and discharges again the molten metal into the furnace 1 thereby stirring the molten metal. A metallic oxide 13' deposits near a communicating hole 2 upon repetition of such operation. The suction and discharge by the cylinder 4 are thereupon suspended and a high-pressure inert gas valve 20 provided to an air vent pipe 8 so as to branch therefrom is opened to introduce a high-pressure inert gas into the cylinder 4. The high-pressure inert gas discharges forcibly the metallic oxide 13' deposited near the hole 2 into the furnace 1.