Method and apparatus for preparing specimen

A method and apparatus for reliably preparing a good thin-film specimen (3) adapted for TEM (transmission electron microscopy) observation is offered. The apparatus has a high-brightness pixel extraction unit (10) for extracting high-brightness pixels (P nm ) which form a specimen image taken by an imaging unit (8) and which have intensities becoming greater than a given threshold value as the specimen is thinned. The apparatus further includes a decision unit (11) that makes a decision as to whether the high-brightness pixels extracted by the high-brightness pixel extraction unit form a continuous sequence of pixels whose number is in excess of a given number on the specimen image. If the decision is affirmative, the decision unit sends a signal to an ion gun control unit (12) to stop the ion-beam irradiation of the specimen.