PURPOSE: To obtain an inexpensive measuring method with high safety by receiving an ultrasonic reflected echo reflected by the tip surface of a wire in contact with the surface of molten steel and measuring the level of the molten steel on the basis of the time difference between transmission and reception.

CONSTITUTION: The steel wire 5 is uncoiled from a drum 4 to the surface of the molten steel 3 in a mold 1 by pinch rollers 7 and 7 through a supply driving motor 6. An ultrasonic wave transmitter and receiver 8 provided at a specific position relative to the wire 5 is connected to a signal processor 9, which is supplied with a wire supply speed signal and a wire consumption signal from the supply driving motor 6 and with a constant, coefficient, etc., from a setter 10. The output signal of the signal processor 9 is supplied to an indicator 11, controller 12 for a sliding nozzle 2, and motor controller 14 for controlling a pinch roller for ingot piece drawing and a strainer roller through a molten steel level regulator 13 respectively.