To remove a harmful material such as dioxin at a high efficiency by sucking a waste gas from an electric melting furnace, adsorbing the harmful material such as dioxin in the waste gas on a carbon based adsorbent and charging the adsorbent, on which the harmful material is adsorbed, to the electric melting furnace as a first-in material to treat it.

In the operation of an electric melting furnace 1 in a steel making plant, a waste gas sucked from the electric melting furnace by an air blower 18 is passed through a combustion column 13 to execute CO combustion or the like and cooled through a cooling column 14 and after that, dust containing dioxin, heavy metals or the like is collected by a bag filter 15. Then, activated carbon is blown into the waste gas from a charging device 18 to adsorb dioxin and the heavy metals to the activated carbon and the activated carbon is collected by a bag filter 17 at the down stream side. Then, the activated carbon collected by the bag filter 17 and gathered by a dust transporting conveyer 30 is charged into the electric melting furnace 1 as a first-in material or a carbon injection material to thermally decompose the harmful material such as dioxin.