PURPOSE: To prevent an insulating substrate from being charged electrostatically with an electron beam which is projected by a scan type electron microscope by covering the capillary exposure part of the insulating substrate exposed in the surface of the sample with conductive liquid by utilizing capillarity.

CONSTITUTION: Linear patterns 2 and 3 of the substrate 1 are irradiated with the electron beam and its secondary electron beam is detected to obtain the images of the patterns 2 and 3. In this case, the conductive liquid 9 is dripped previously between the substrate 2 and 3 of the pattern 1. The dripped conductive liquid 9 moves forth in the capillary exposure part 4 between the patterns 2 and 3 to cover the entire area of the substrate. Consequently, the substrate 1 can be prevented from being electrostatically charged with the electron beam which is projected by the scan type electron microscope, so accurate images can be observed without lowering the acceleration voltage of the electron beam of the electron microscope.