Method and equipment permitting one to easily prepare a good thin-film specimen adapted for observation are offered. The equipment has an ion gun tilted left and right repeatedly to etch a specimen material by an electron beam tilted left and right by 1.5.degree. about the z-axis. Then, the ion gun is tilted left and right plural times to ion etch the specimen material. Since a portion of the specimen material is especially heavily etched, a through-hole is formed in the specimen material. A thin film having a thickness of about 100 .ANG. is formed around the through-hole. This thickness is adapted for TEM (transmission electron microscope) observation.