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 CF.sub.4 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.

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 CF.sub.4 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.

There is provided an ion milling apparatus that can enhance reproducibility of ion distribution. The ion milling apparatus includes an ion source 101, a sample stage 102 on which a sample processed by radiating a non-convergent ion beam from the ion source 101 is placed, a drive unit 107 that moves a measurement member holding section 106 holding an ion beam current measurement member 105 along a track located between the ion source and the sample stage, and an electrode 112 that is disposed near the track, in which a predetermined positive voltage is applied to the electrode 112, the ion beam current measurement member 105 is moved within a radiation range of the ion beam by the drive unit 107, in a state in which the ion beam is output from the ion source 101 under a first radiation condition, and an ion beam current that flows when the ion beam is radiated to the ion beam current measurement member 105 is measured.

The disclosure provides a method for preparing a cross-section of a sample by milling with a focused ion beam. The cross-section is to be prepared at a pre-defined position. The method includes excavating a trench by milling in a first milling direction. The first milling direction leads away from the position of the cross-section to be prepared. The method also includes excavating the cross-section by enlarging the trench by milling in the reversed milling direction. The second milling direction leads towards the position of the cross-section to be prepared, whereupon the milling is completed at the position where the cross-section is to be cut. The desired largest milling depth is achieved at the completion of this milling step.