Provided is a timing controller configured to operate a display device. The timing controller includes a receiving unit receiving a still image signal; a transmitting unit outputting an output data used to display images; a clock frequency spreader generating a spread clock signal having a frequency value adjusted between first and second frequency values by modulating a reference clock signal; a memory system storing a first image data which corresponds to a first frame of an image, and outputting the first image data in response to the spread clock signal; and a still image managing unit communicating with the memory system in order to output the first image data as the output data. According to the timing controller, electro-magnetic interference may be reduced and operation errors of the display device may be prevented.