PURPOSE: To prevent the pollution on the surface of an electronic optical system, facilitate cleaning, and reduce the number of cleanings by providing a surface film made of either one of TiN, TiC and BN on the surfaces of components of the electronic optical system of a scanning electron microscope.

CONSTITUTION: A film 32 made of TiN, TiC or BN is formed on the surfaces of an electron gun cartridge 1, slits 7 and 10, and slit ties 5, 8, 11 severely polluted in particular among components of an electronic optical system. These components are made of stainless steel or brass. The evaporated materials from the tungsten filament of the electron gun and an analysis sample radiated by an electron beam are hardly stuck on the surface of the electronic optical system, and cleaning is facilitated when they are stuck.