To provide a treatment method of a contaminated gas and a rotary kiln for manufacturing cement, free from shortage of main fuel and oxygen necessary for burning the main fuel, even when a supply quantity of the contaminated gas is increased, capable of keeping stable flame and burning zone temperature, and manufacturing the cement without giving bad influence on its quality in accompany with combustion decomposition of the contaminated gas, even when the supply quantity of the contaminated gas is significantly increased.

In this treatment method of the contaminated gas, the contaminated gas P decomposable under high temperature atmosphere, is jetted to a position separated from the flame of the main fuel burner, by using an injection pipe 2 mounted independently from the main fuel burner 1, to be supplied into the rotary kiln, when a cement clinker C is manufactured by burning a cement material while keeping the inside of the rotary kiln 3 for manufacturing cement under high temperature atmosphere by the main fuel F and oxygen O2 supplied from a main fuel burner 1.