PURPOSE: To prevent the degradation in the quality of an ingot owing to inclusion of slag in the stage of receiving molten metal in a vessel by detecting the oscillations of the vessel which increase temporarily upon inflow of the slag and stopping the charging electrically, automatically and quickly.

CONSTITUTION: In the stage of charging the molten metal 3 on which slag 16 is afloat into a tundisch 4 through a ladle nozzle 2 from a ladle 1, the oscillations of the tundish 4 increase temporarily upon inflow of the slag 16 into the tundish 4. The oscillations are detected with an oscillation detector 7 mounted to the tundish 4 and are outputted as a signal. After the output is amplified with an amplifier 8, it is converted to oscillation components with a coverter 9, and further the oscillation components by external factors are removed with a filter circuit 10. The output thereof is passed through a smoothing circuit 11a and an output device 11, and is outputted as the smoothed signal to an operator 12. Here, the signal that receives the oscillation signal output higher than a reference value is outputted to an output device 13 for stopping of charging, by which a charging controller 14 and a machine 15 for opening or closing the ladle nozzle is operated to close the nozzle 2.