PURPOSE: To provide an inexpensive and thin polarization device efficiently fetching light close to linear polarized light.

CONSTITUTION: A frame body 31 is provided with an incident window 32 and an emitting window 33 and filled with a transparent body 34. Then, polarization selective mirrors 35 and 36 and mirrors 37 and 38 are arranged in the frame body 31 so that the cross sections thereof become zigzag with respect to an optical axis 30. When the natural light beams 39 and 40 made incident on the polarization device is respectively made incident on the mirrors 35 and 36 from the window 32, the P polarization components 41 and 42 thereof are transmitted and the S polarization components 43 and 44b are reflected. Then, the components 41 and 42 are emitted from the window 33 and the components 43 and 40 are reflected on the polarization and separation mirrors 35 and 36 again and emitted from the window 32 after they are reflected on the mirrors 37 and 38.