Abstract: It is an object to provide a cleaning method in a CVD apparatus capable of efficiently removing a by-product such as SiO2 or Si3N4 which is adhered to and deposited on the surfaces of an inner wall, an electrode and the like in a reaction chamber and the side wall of a piping of an exhaust path or the like at a film forming step, in which the amount of a cleaning gas to be discharged is very small, an influence on an environment such as global warming can also be lessened and a cost can also be reduced.