In accordance with the present invention, there is provided a treat chlorine bypass dust while preventing increases in chemical cost and concentrations of heavy metals in clinker, and ensuring stability in quality of cement. In a chlorine bypass facility 1 extracting a part G of combustion gas, while cooling it, from a kiln exhaust gas passage, which runs from an inlet end of a cement kiln to a bottom cyclone, and recovering a high chlorine concentration chlorine bypass dust D5 from the extracted gas G1, a slurry S containing chlorine bypass dust and SO2 gas or/and CO2 gas are contacted with each other to obtain solid content. The slurry containing chlorine bypass dust and an exhaust gas from the chlorine bypass facility or/and the exhaust gas from the cement kiln can be contacted with each other, and the solid content can be fed to a cement finishing process, which allows cement with low CaO and Ca(OH)2 contents and with stable property such as setting time to be produced.