PURPOSE: To control and restrain the variation of molten metal surface according to respective cases by distingushing and detecting the variation of the molten metal surface caused by the variation of molten metal vol. and the variation of the molten metal surface caused by free vibration of the molten metal in a mold.

CONSTITUTION: Two sets of eddy current type molten metal surface level meters 6, 7 arranging transmitting coils 6a, 7a and receiving coils 6b, 7b so as to mutually part the specified interval, are faced on the molten metal surface in the mold 1. The arranging direction of the transmitting coil 6a and the receiving coil 6b at the one side is paralleled to a long side of the mold 1 respectively and the arranging direction of the transmitting coil 7a and the receiving coil 7b at the other side is paralleled to a short side respectively. The variation of the molten metal surface caused by the variation of the molten metal vol. and the variation of the molten metal surface caused by the variation of the molten metal in the mold 1 are obtd. by distingushing based on the detected values and the difference between both molten metal surface level meters 6, 7 and the opening degree command is outputted to an opening degree setter 8 of a hydraulic cylinder 4 so that the molten metal surface varied with the variation of the molten metal vol. matches up to the preset aimed value. Further, an arithmetic control device for outputting control signal to an electromagnetic brake 5 is provided so as to restrain the variation of the molten metal surface based on the vibration of the molten metal.