A photoinduced refractive-index changing region is formed by irradiating while focusing a single beam of pulse laser light having an energy amount to cause a photoinduced change in refractive index onto a light guide of an optical element such as a lens, a mirror, a diffraction grating, a polarizer, or a wavelength filter. In the photoinduced refractive-index changing region, since the refractive index is periodically changed in one direction, of the light propagating through the optical element, only a polarized light penetrates through this photoinduced refractive-index changing region. Accordingly, the photoinduced refractive-index changing region can be functioned as a polarizer.