PURPOSE: To automate the supplying of molten steel into a triangular ladle and reduce the variation to the aimed level of molten metal surface height, at the time of supplying the molten metal into the triangular ladle up to an objective level by tilting a stationary ladle.

CONSTITUTION: While the molten metal surface level has no influence on the molten metal supplying quantity till detecting the molten metal surface at the low level position set in the triangular ladle 1 with a first detector 4, the stationary ladle 2 is tilted at high speed. Thereafter, the stationary ladle 2 is tilted at low speed till detecting the molten metal surface at the high level position set at the suitably lower position than the aimed level 6 with a second detector 5, and thereafter, the stationary ladle 2 is tilted back at high speed. In such a way, the molten metal surface level is precisely detected and controlled.