A degradation compensating device includes an accumulator configured to accumulate stress data every pixel block, a memory configured to receive the stress data from the accumulator, and to load accumulated data from an external flash memory when a display device power is turned on, the accumulated data being a total sum of the stress data, a compensation factor calculator configured to determine a target compensation factor based on the accumulated data to compensate image data, and to apply an initial compensation factor to the target compensation factor during a wake-up period after loading the accumulated data is completed, the initial compensation factor being changed gradually during the wake-up period, and a data compensator configured to generate image compensation data based on the target compensation factor, and to generate initial image data based on a wake-up factor that is an adjusted target compensation factor based on the initial compensation factor.