A polishing technique wherein scratches, peeling, dishing and erosion are suppressed, a complex cleaning process and slurry supply/processing equipment are not required, and the cost of consumable items, such as slurries and polishing pads, is reduced. A metal film formed on an insulating film having a groove is polished with a polishing solution containing an oxidizer and a substance which renders oxides water-soluble, but not containing a polishing abrasive.