A cleaning method is provided. In the cleaning method, a cleaning gas is supplied into a processing chamber, a radio frequency (RF) power for plasma generation is applied to one of a first electrode on which a substrate is to be mounted and a second electrode disposed to be opposite to the first electrode in the processing chamber, and a negative voltage is applied to an edge ring disposed to surround the substrate. Further, plasma is generated from the cleaning gas and a cleaning process using the plasma is performed.