A de-coating method includes: exposing a coated body in which a coating made of an inorganic material is formed on a surface of the metal body to ion flows to peel off the coating from the metal body, wherein the coated body is placed at an ion flow-concentrated portion where two or more ion flows overlap each other, and is exposed to the ion flows without addition of a positive or negative bias to the coated body. As gases for use in generating ions from plasma, oxygen and CF4 that promote de-coating through a chemical reaction are preferably used in addition to Ar that performs de-coating under the physical action of ion collision and stabilizes plasma.