PURPOSE: To shorten the measuring time and provide precise measurability by diverging a light flux from a specimen into two fragments by a beam splitter, synthesizing an image from focused images on their image points, and thereby performing checking of the part to be measured without requiring movement of a shield mask.

CONSTITUTION: A beam splitter 15 is furnished behind an objective mirror 3 to form two divergent light paths, and specify shield masks 10, 11 are provided only on one of the light paths at its image point. The beams of light on the two divergent light paths are monitored by respective cameras 20, 21 in positions behind their image points. Signals given by these TV cameras 20, 21 are fed to an image processing device 22, and the focused images at the image points are synthesized in a screen to serve monitoring. According to this constitution. the position relationship between parts to be measured over the whole specimen 2 can be made clear without requiring movement of the shield masks 10, 11, and change of the part measured be made easily, which should shorten the measuring time greatly and also enhance the measuring accuracy.