PURPOSE: To realize three-dimensional vertical visual field through a sample by using longitudinal-direction chromatic aberration and lateral-direction chromatic aberration in relation to a color dispersion prism in a binocular eyepiece assembly.

CONSTITUTION: A pair of direct-vision dispersion prisms 6 and 7 is arranged between a scanning device and an image-formation device along the axis of a light beam reflected so that various wavelength light beams may be separated in the image-formation device. A beam splitter 14 turning the reflected light beam to the respective prisms 6 and 7 along different paths is provided. An objected lens 3 having the primary longitudinal-direction chromatic aberration enough to give the depth of focus by which a distinct image is formed in an observation station concerning the different distances of the prisms 6 and 7 from the observation station concerning respective colors of the sample reflected from the different depth of the sample is provided.