PURPOSE: To realize a secondary electron image observation method in which even a bottom part of a contact hole or the like formed in a manufacturing process of a semiconductor device can be observed clearly.

CONSTITUTION: A control device 13 controls an acceleration voltage control unit 2, and it sets acceleration voltages in order. An electron beam scans in line at a sample part where a trench is formed while changing the acceleration voltage of an electron beam EB. Secondary electrons generated in accordance with scanning are detected, and detection signals are supplied to a cathode-ray tube 12, therefore an image of the acceleration voltages different along the height of an image surface formed by radiation of the electron beam are displayed. An observer observes this image, each part in a sample is displayed in grey, the acceleration voltages with which both a surface part and a bottom part of the trench are indicated to the control device 13, and observation of a desired range of the sample after this is performed by the electron beam of the acceleration voltages.