PURPOSE: To facilitate the confirmation of the grade of vacuum by indicating the grade of vacuum in the body to be exhausted on the indicator for indicating the image of specimen.

CONSTITUTION: The inside of mirror 1 is exhausted by vacuum pump 2 and the grade of vacuum is measured by vacuum meter 3. The output from secondary electron detector 4 for detecting the secondary electron emitted from the surface of specimen when scanning on the surface of specimen with focused electron beam in two dimension is provided through signal amplifier 5 to signal switching circuit 6, to indicate the image of specimen on cathode ray tube 7 in accordance with the operation of said signal switching circuit and to indicate the grade of vacuum in mirror body 1. Consequently the confirmation of vacuum in the body is facilitated.