PURPOSE: To enhance the quality of slag along with the treatment of dust, by treating dust generated from an electric furnace with slag held under a high temperature molten state.

CONSTITUTION: The titled apparatus consists of a dust collector 2 for collecting dust, a treating slag ladle 14 for receiving slag A, a dust treating chamber 11 and a dust collecting chamber 22. A bubbling gas blow-in member 17 is attached to the treating slag ladle 14 and slag A is introduced thereinto while bubbling gas is blown into the slag A to convey said slag A to the dust treating chamber 11. The dust collected by a dust collector 2 is thrown into the treating slag ladle 14 along with a collapse preventing and reaction promoting additive C added if necessary to mix by stirring. A part of the dust is reduced and vaporized to be recovered by the dust collector 2. The remainder is immobilized in the slag A and cooled in the dust collecting chamber 12 to be discharged along with the slag A.