Abstract: A stereomicroscope comprising an objective lens, an afocal vari-focal optical system disposed coaxially with the objective lens, a pair of right and left imaging optical systems for imaging parallel rays emerging from the afocal vari-focal optical system, and right and left eyepiece lens systems for magnifying images which are formed by the right and left imaging optical systems.This stereomicroscope permits observing images with adequate stereoscopic impressions and can be relatively compact owing to a fact that the microscope satisfies the following condition (1):0.005 .ltoreq.AD.multidot..beta./f.sub.0 .ltoreq.0.