A viewing area adjusting device has an image pickup unit capable of shooting a forward direction of a stereoscopic video display device capable of displaying a stereoscopic video, a viewer information detector configured to detect the number of viewers and positions of the viewers by a video shot by the image pickup unit, a viewing area adjustment policy determining unit configured to select any one of a plurality of viewing area adjustment policies based on the number of viewers detected by the viewer information detector, a viewing area information computing unit configured to compute an adjustment amount for the viewing area, and a viewing area adjusting unit configured to adjust the viewing area.