A method of driving an image display device including (A) an image display panel in which pixels each having first to fourth subpixels displaying first to third primary colors and fourth color, respectively are arranged in a two-dimensional matrix, and (B) a signal processor, in an i-th image display frame, in the signal processor, first to fourth subpixel output signals are obtained on the basis of at least first to fourth subpixel input signals and a corrected expansion coefficient α′i-0, and output to the first to fourth subpixels, respectively, the maximum value Vmax(S) of luminosity with saturation S in an HSV color space is obtained in the signal processor or stored in the signal processor, and in the i-th image display frame, in the signal processor, (a) saturation Si and luminosity Vi(S) in pixels are obtained, (b) an expansion coefficient αi-0 is obtained, and (c) the corrected expansion coefficient α′i-0 is determined.