A display device includes: a gain provider configured to set a time point elapsed by a set period from a time point at which a first region of an input image is detected as a still region, as a set time, and to gradually decrease a gain value from the set time; and a grayscale converter configured to generate an output image by applying the gain value to the first region and a second region including a peripheral region of the first region among the input image, wherein the gain provider is configured to set the set period differently according to size of grayscale values in the first region.