PURPOSE: To detect and regulate the surface of the bath of molten metal from a difference from a preset target value by introducing an inert gas into the molten metal, measuring the percolation and absolute pressure value thereof and determining the spacing from the place of introduction to the surface of the bath from the difference between the measured absolute pressure value and the pressure acting on the surface of the bath.

CONSTITUTION: The inert gas is supplied via a throttle valve 1 to a percolation controller 2, from which the inert gas arrives at a pipe 4 via a conduit 3. The pressure detected by a pressure measuring instrument 5 connected to the conduit 3 is the scale for the spacing of the surface of the bath of the molten metal from an inert gas introducing pipe. The pressure measuring instrument converts the detected pressure to an electric signal and supplies the actual value thereof to a comparator 6. The comparator forms a regulation signal from a difference from the preset target value and supplies the signal to a regulation device 7. The regulation device actuates a closing plug 8 of a distributor 9. As a result, the easy and reproducible detection and regulation of the surface of the metal bath are made possible.