The present invention provides a method and an apparatus for treating a chlorine-containing waste, which can separate and recover a chlorine component from a chlorine-containing waste, and also can achieve a high chlorine removal thereby obtaining a high purity chlorine compound, and can decrease the amount of water for recovering chlorine. The method for treating a chlorine-containing waste of the present invention comprises a washing/filtrating step of adding water to the chlorine-containing waste, followed by mixing to form a first slurry, separating the first slurry into a solid and a filtrate through filtration, and using the resulting solid as a cement raw material; a filtrate treating step of adding a reducing agent and a pH adjustor to the filtrate to form a sediment containing heavy metal and calcium contained in the filtrate, and separating the sediment through filtration; a crystallization step of concentrating the filtrate, from which the sediment has been removed, through heating and evaporation to form a second slurry in which a chlorine compound contained in the filtrate has been crystallized, separating the second slurry into a solid containing a chlorine compound and a mother liquor, and recovering the solid; and a separated mother liquor treating step of returning a portion of the mother liquor to a cement manufacturing facility.