The present invention relates to a display device and a control method therefor, and involves the concept of controlling a display to reduce luminance from a default luminance to a first luminance for a first reduction time when brightness of a fixed area is maintained for a first predetermined time or more, and controlling the display to increase the luminance from the first luminance to the default luminance, when a set-top box receives, from an external device within a second predetermined time, a first signal for changing a screen from a first screen to a second screen.