PURPOSE: To prevent the deterioration of molten metal and improve cleanliness by inputting heat to the molten slag in a well and stirring the molten metal.

CONSTITUTION: The outflow port 5a of a well 5 is closed with a stopper 6, and a required amount of molten slag (a) is poured into the well. Thence, molten metal is poured into the well 5 from a ladle 7. During pouring into the well 5 or upon completion of the pouring, electrodes 9a, 9b are immersed in the molten slag (a) in the well 5, and current is supplied. At the same time, the molten metal (b) is stirred by the magnetic force of a molten metal stirrer 11. This prevents the molten metal (b) in the well 5 from being solidified by heat extraction and maintains the temp. in the molten metal (b) uniformly. Even more, the activity of the molten slag is enhanced thus leading to enhanced refining effect. After the completion of the treatment of the molten (b) in the well 5, the stopper 6 is removed to allow the molten metal (b) in the well 5 to flow into the mold inside 2.