PURPOSE: To prevent hot-dipping of a ladle by arranging a temp. sensor between the end part of a lifter and the tip part of an electrode for detecting molten metal surface and forcedly returning back the lifter after the temp. sensor detects the molten metal surface.

CONSTITUTION: The lifter 2 descends the ladle 1 and when the electrode sensor 3 detects the molten metal surface A', the descending is stopped. When the electrode sensor 3 executes the erroneous detection and the lifter does not stop and further descends, the measuring temp. is gradually risen as the temp. sensor 4 approach the molten metal surface A', and at the time of becoming the prescribed temp., the descending of the lifter 2 is stopped and the lifter is forcedly returned upward to the original position and also an alarm to display that the electrode sensor 3 is in some trouble is displayed. The hot-dipping accident of the ladle can be prevented.