A display device is provided that controls, considering affection due to a watcher's age and his viewing distance as human-visual characteristics, a display-screen brightness level at which the watcher does not feel glare. The display-screen brightness is most suitably set by simple calculation using relationships among watcher's ages, display sizes, glare levels, and screen-illuminance levels, etc. obtained by a subjective-assessment experiment. According to this display device, considering watcher's various conditions such as the age, the visual acuity, and the viewing distance, even if the watcher watches the display for a relatively long time, the watcher does not feel tiredness; thus, comfortable watching can be achieved.