The rotation axis of each mirror of a DMD (4) defines an angle of 45° with respect to long and short sides of a rectangular image display area. A polarization conversion optical system (24) makes a polarization direction of light from a light source (1) arranged in one direction and projects the arranged light, and after total reflection from the critical surface (31b) of a TIR prism (3), the light is guided to the DMD (4). When the incident surface of the critical surface (31b) and the mirror incident surface of the DMD (4) are in parallel with each other, a PBS prism array of the polarization conversion optical system (24) carries out the polarization and separation of the light from the light source (1) in a direction corresponding to the long side direction of the image display area of the DMD (4) in the case of the separation of the light from the light source (1) into two linear polarizations having different polarization directions. A polarization control means makes the two linear polarizations after the polarization and separation arranged in parallel or vertical polarization directions with respect to the incident surface of the critical surface (31b) and projects the same. Thus, a polarization condition of the light for illuminating the DMD (4) can be prevented from falling into disorder at a reflecting surface in the optical path, so that a light amount of the projection image can be prevented from reducing.