A medical stereo observation system includes a stereo imaging unit producing a first image for a left eye and a second image for a right eye that mutually have parallax and a stereo display unit capable of displaying stereoscopically the images produced by the stereo imaging unit. The stereo imaging unit has a first imaging optical system producing the first image for the left eye and a second imaging optical system producing the second image for the right eye, and focal positions of these imaging optical systems are located far away from the intersection of optical axes of the imaging optical systems, viewed from the stereo imaging unit. Whereby, a large-depth space can be comfortably observed in a wide range and a viewer can observe an observation object without bringing about a feeling of fatigue.