A stereoscopic image observing apparatus includes a right-eye projector 1 and a left-eye projector 2 which illuminate projected light for right and left eyes with the parallax generated based on an image pick-up signal obtained from a stereoscopic endoscope 8, a Fresnel lens 17 which applies and reflects the lens operation with the positive polarity to the projected light of the illuminated images for the right and left eyes, and an optical shift element layer 16 having liquid crystal 20 and a double refraction plate 19 for changing and diffusing on time series the reflecting position of the reflected light of the images for the right and left eyes from the Fresnel lens 17.