PURPOSE: To obtain efficient lighting of linear polarization with simple and compact constitution by splitting light from a light source for illumination into two by a polarization beam splitter, guiding one as it is as illumination light and making the other incident on the polarization beam splitter again after rotating its polarization direction by 90°, and mixing both light beams.

CONSTITUTION: The light from the light source 20 for illumination is split by the polarization beam splitter 21 into two, i.e. P polarized light component and S polarized light component; and the P polarized light component is reflected by the polarization beam splitter 21 and used as the illumination light. The S polarized light component, on the other hand, is reflected by a reflecting part 22 and transmitted through the polarization beam splitter 21 again, and the light is transmitted through a λ/4 plate 23, reflected by a reflecting mirror 24, and transmitted through the λ/4 plate 23 again. At this time, the S polarized light component has its polarization direction rotated by 90° and becomes P polarized light, so this when incident on the polarization beam splitter 21 again travels in the same direction with the former P polarized component and is used as illumination light.