PURPOSE: To attain superior cleanability and to nearly prevent the generation of a malodor by treating a filter with a stuck polyphenylene sulfide-based polymer in an org. solvent contg. chlorosulfonic acid.

CONSTITUTION: A filter and a filter device with a stuck polyphenylene sulfide- based polymer is treated in an org. solvent contg. chlorosulfonic acid. The solvent may be dichloroethane, chloroform or pyridine, etc. Therefore, not only the polymer in the filter and the filter device is completely removed, but also the generation of a malodor due to the decomposition of the polyphenylene sulfide at the time of cleaning is nearly prevented and environmental pollution is well controlled.