1. A naked-eye stereoscopic display apparatus comprising: a display device comprising a plurality of pixels arrayed in a horizontal direction and a vertical direction and a memory store for storing data representing the plurality of pixels, whereby the display device assigns respective pixels of video data composed of a plurality of viewpoint images to the plurality of pixels, thereby displaying the respective pixels of pixel data; an optical light directing means comprising an optical member that has a plurality of optical elements periodically arrayed therein, arranged on the display device in a state where a periodic direction of the optical elements is inclined with respect to the horizontal direction of pixels in the display device, and configured to divide the plurality of viewpoint images displayed on the display device into a plurality of different viewpoint directions, and to present the divided viewpoint images; and a viewpoint adjustment unit comprising a processor, the processor storing viewpoint adjustment data, receiving a parallax level derived from the plurality of viewpoint images, and which, within a maximum predetermined horizontal viewing angle defined by two viewpoint images with the largest parallax, defines a first horizontal angular region, comprising a left region in which there is a high possibility that a viewer's left eye may be present when observing the display device and a right region in which there is a high possibility that a viewer's right eye may be present when observing the display device, and a second horizontal angular region in which there is a low possibility that the viewer's left eye and the viewer's right eye may be present, and configured to reduce the parallax between adjacent viewpoint images displayed in the first horizontal angular region more than the parallax between adjacent images in the second horizontal angular region.