To provide a compact polarization changing optical device which is provided with two light source lamps and emitted light quantity is effectively utilized, that is, a final luminous flux can be made to exit to a rectangle area with an ultimate aspect ratio of about 1:2, for example.

This device is provided with a first polarization changing part having a light source 10, a first polarizing beam splitter dividing a first luminous flux made to exit from the light source 10 horizontally forward into transmitted light and reflected light advancing in a direction orthogonally crossing with the transmitted light, a first total reflection mirror making the reflected light exit from the first polarizing beam splitter horizontally forward, a second polarizing beam splitter dividing a second luminous flux made to exit in the direction orthogonally crossing with the first luminous flux made to exit from the light source into a reflected luminous flux advancing horizontally forward and a transmitted luminous flux, and a second total reflection mirror reflecting the transmitted luminous flux from the second polarizing beam splitter horizontally forward, and provided with a second polarization changing part having the same constitution as that of the first polarizing changing part, and the first polarization changing part and the second polarization changing part are arranged on a position which is point-symmetric.