A wide-band wave plate having at least two wave plates, each of which has
a microstructure to generate a phase difference, the microstructure
having a cycle not shorter than 1/n.sub.min of a shortest wavelength of
light in use, wherein the two wave plates are arranged to face opposite
with their main axes in non-parallel with each other, wherein n.sub.min
is a refractive index of a wave plate material with respect to the
shortest wavelength.
