PROBLEM TO BE SOLVED: To automatically decide whether a field of view picked up is a field of view suitable for retrieval of the intended form to efficiency extract only the necessary field of view. SOLUTION: The state of a field of view is decided (S17), by a method of preparing a line profile of the field of view picked up to measure brightness (gradation), a method of determining the cross-correlation between two transmission images of the same field of view, taken with electron-optical conditions varied to find the degree of coincidence (correlation function) between them or a method of determining the phase-limited correlation between two transmission images taken with conditions varied to find the degree of coincidence between them, thereby transferring to the next field of view, when the field of view decided as being not suitable for observation/retrieval.
