PURPOSE: To obtain a method to find out accurately and easily a part to be re-observed, by supplying a gas containing metal compound, irradiating, via the gas, the vicinity of a part to be observed with a converged ion beam when output energy is adjusted, and forming a metal mark thereon.

CONSTITUTION: When the part 2 to be observed of a semiconductor device 1 to be observed is irradiated with primary ion beam 3, secondary electron 4 is excited and emitted from the part 2 to be observed, and the part 2 to be observed is examined by detecting the secondary electron with an electron microscope. In the case where the later re-observation is required, a gas 8 containing metal compound such as tungsten and molybdenum is supplied to the vicinity of the part 2 to be observed, and, via the gas 8, the vicinity of part 2 to be observed is irradiated with a converged ion beam 6, to form a mark 7. On the occasion of re-observation, the part is irradiated with primary ion beam 3, and then a lot of secondary electrons are excited and emitted from the mark 7. By detecting them with a secondary electron microscope, the position of the mark 7 can be easily recognized. Thereby, the part 2 to be observed necessary for re-observation can be easily found out.