To reduce the cost of a reducing material to be used for a dust treating device for separating and recovering metal such as lead and zinc, and other materials from the dust stuck to a dust collecting device, etc., of an arc furnace for steelmaking.

In this dust treating device, the metallic oxide in the dust 50 are reduced to vaporize the metallic components by mixing metallic powdery reducing material 51 such as iron powder with the dust 50 containing metallic oxide and heating and stirring them in a closed vessel 1, and the metallic components in gas are recovered by cooling the exhaust gas from the closed vessel 1. In this case, the reducing material 51 to be mixed with the dust 50 is brought into contact with a high reducing material such as carbon monoxide, hydrogen or powdery carbon in a storage hopper 3 to strengthen the reducing capacity of the reducing material, and thereafter, this material is mixed with the dust 50.