1. An image display device comprising:a communication unit that transmits a transmission request to each of a plurality of image transmission devices and that receives a frame that includes a differential data that is transmitted by each image transmission device in accordance with said transmission request, said differential data indicating differences between images that are displayed continuously in time;
a display unit that displays an image based on said differential data that is contained in said frame that is received from each of said image transmission devices;
a measurement unit that, for each of said image transmission devices, measures a first required time interval that is required from a start of transmission of said transmission request until a start of reception of said frame and a second required time interval that is required from the start of reception of said frame until an end of reception of said frame; and
a control unit that controls a transmission operation of said transmission request of said communication unit;
wherein said control unit causes transmission of said transmission request to each of said image transmission devices from said communication unit at a transmission interval that has been set in advance, causes said measurement unit to carry out measurement of said first and second required time intervals for each of said image transmission devices, and changes the transmission interval of said transmission request based on a result of said measurement.