A DMD (4) as a image display device time divisionally displays channel
images formed by separating an image into RGB channels. A white light
emitted from a xenon lamp (1) is separated, by an acousto-optical element
(3), into spectal components. Those spectal components are projected onto
the DMD (4). A refractive index of the acousto-optical element (3) varies
with a frequency of an ultrasonic wave applied thereto. Therefore, a color
of the spectral component applied to the DMD (4) may be changed by varying
the refractive index of the acousto-optical element. RGB monochromatic
lights may be irradiated on the DMD (4) by setting the frequencies
F.sub.R, F.sub.G, F.sub.B of the ultrasonic wave at appropriate values.
