PURPOSE: To improve the detecting accuracy of molten metal surface level at the initial stage of the starting of supplying the molten metal into a mold.

CONSTITUTION: A vortex type level sensor SE1 together with a laser beam type or an ultrasonic type molten metal surface level sensor SE2 are arranged above a mold 1 and the molten metal surface level is detected with the laser beam type or the ultrasonic type molten metal surface level sensor SE2 in the starting treatment of supplying the molten metal into the mold 1. The molten metal surface level control and the charging time of powder are decided based on this detected value. Further, when the molten surface level rises within the detecting distance of the vortex type molten metal surface level sensor SE1, the molten metal surface level control and starting time of drawing out of a dummy bar head 4, etc., are decided based on the molten metal surface level detected value with the vortex type molten metal surface level sensor SE1.