A charged beam apparatus comprises a source tank provided outside the column and containing a plasma source, a plasma generating apparatus for generating plasma from a plasma source supplied from the source tank, gate valves and an exhausting pump for introducing plasma generated by the plasma generating apparatus into the column and for exhausting the plasma therefrom, and an O-ring for restricting a passage of plasma in the column such that those portions of cleaning portions to be cleaned to which internal contaminants stick are mainly exposed to plasma. Therefore, it is possible to generation of an oxide film, a fluoride film, or the likes which cause drifting can be restricted.