PURPOSE: To facilitate the positioning of the tip arrangement of the sample by providing a scanning electron microscope having a beam blanking device and an optical microscope with a pair of optical microscopes which are parallel to the electro-optical axis.

CONSTITUTION: On both sides of the electro-optical axis of a scanning electron microscope having a beam blanking 14, a pair of optical microscopes 7 and 7' are installed parallel to the electro-optical axis. Next, the orifice 2 of a semiconductor wafer 1 used as a sample is positioned on a device 6 for minutely moving the sample. After that, signals from ITV cameras 8 and 8' are displayed on an ITV monitor 10 through a switching circuit 9 and the end surfaces of the right and the left tips of the sample are accurately positioned by controlling the R-axis of the minute device 6, thereby performing the positioning of the sample while the beam blanking 14 is in the state of its operation. As a result, it is possible to perform accurate observation and accurate measurement of the length of the pattern by a simple operation without performing any electron ray irradiation.