A disclosed control device includes a first unit configured to generate image data of multiple images to be superposed one on the other to form a single image and transmit the image data. The second control unit transmits to the first control unit a horizontal sync reference signal for achieving synchronization of the images in a horizontal direction. Based on the horizontal sync reference signal, the first control unit transmits to the second control unit a transfer clock signal that indicates transmission timing of the image data and an effective area signal that indicates an effective area of the image data. The first control unit asserts the effective area signal for an effective-area-signal assertion period that occurs between two consecutive reference-signal assertion periods during which the horizontal sync reference signal is asserted.