To obtain and maintain a good polishing characteristic by restraining a polishing slurry from evaporation, and to avoid increasing in the consumption of the polishing slurry accordingly, when a polishing object is subjected to a CMP treatment.

By using a polishing pad 4 having a polishing surface with a larger area than the surface to be polished of a polishing object 1, the surface to be polished and the polishing surface are relatively slid, with polishing slurry interposed between the surface to be polished and the polishing surface. Thus, an exposed part in the polishing surface of the polishing pad 1 in a polishing device for polishing the surface to be polished, is covered by a plate member 6 for restraining the polishing slurry from evaporation.