To miniaturize a polarizing element used for a polarized light irradiation apparatus for optical orientation, to reduce the cost of the polarizing element, and to attain miniaturization of the polarized light irradiation apparatus for optical orientation as a whole.

The light from a lamp 1 is made incident on a polarizing element 5, polarized light separation is carried out and the resultant light is made incident on the integrator lens 4. The polarized light emitted from the integrator lens 4 passes through a shutter 6 and a second plane mirror 7, is made into parallel beams of light by a collimator lens 8, and radiated onto a work piece W. As the polarizing element 5, a combination of a plurality of polarized beam splitters 5a is used. The optical elements are disposed so that the shadow generated by the interface of the polarized beam splitters 5a is projected on the boundary lines of the lenses which constitute the integrator lens 4, thereby preventing the reduction of the illuminance on the surface to be irradiated and aggravation of the illuminance distribution. Alternatively, the polarizing element 5 may be provided on the emission side of the integrator lens 4, and the interface of the polarized beam splitters 5a may be disposed in the part where the illuminance of the light emitted from the interface of each lens decreases.