The invention can provide a stereoscopic image display device, which achieves advantages of both a “glasses” device and a “naked-eye” device, while having a small size. When a right-eye image is displayed, a light blocking region forms on the left side of the center line, and when a left-eye image is displayed, a light blocking region forms on the right side of the center line. When the viewer is located in the regions, the right eye views the right-eye image, and the left eye views the left-eye image. Thus, even when the viewer faces stereoscopic display device with naked eyes, the viewer can view the stereoscopic image as long as the eyes of the viewer are located in the light blocking regions. The right and left images are mixed in the region other than the light blocking regions. However, multiple viewers can view the stereoscopic image when wearing the glasses.