An image display system includes a graphic processor which generates an image signal, a control signal, and a variable frequency signal; and a display device which displays an image at a frame frequency corresponding to the variable frequency signal from the graphic processor. The display device includes pixels connected to emission control lines, data lines, and scan lines; a controller which provides reference data including information on reference cycles, which are cycles in which an emission control start signal is output, to the graphic processor, outputs the emission control start signal based on the control signal, and adjusting an output timing of a scan start signal based on the variable frequency signal; an emission driver which supplies emission control signals to the emission control lines based on the emission control start signal; and a scan driver which supplies scan signals to the scan lines based on the scan start signal.