1. An image display device having a display panel, the device being utilized to form an image display system in which a plurality of image display devices are arrayed in a vertical direction to display one image as a whole while an image allocated to each device is displayed via the corresponding display panel, the image display device comprising:a reading processing unit that reads out partial image information of a frame and delays a start of an output of the partial image information by a predetermined period of time from a start of an output of another partial image information of a same frame, the another partial image information being output by another image display device corresponding to a first row of a vertical arrangement, the predetermined period being determined based on a number of the image display devices arrayed in the vertical direction and a row to which the present image display device belongs in the vertical arrangement.