Abstract: In a second lens array 130A of an illumination optical system according to the present invention, the position of curved faces of third minute lenses 132Ab is displaced from the position of curved faces of second minute lenses 132Aa. Such displacement makes the size of a first region W1 on an illuminating area LA, which is irradiated with light transmitted by polarizing separation films 142, substantially equal to the size of a second region W2 on the illuminating area LA, which is irradiated with light reflected by the polarizing separation films 142 and reflection films 144. This arrangement effectively prevents the significant reduction of the illuminating efficiency occurring in a prior art illumination optical system that utilizes a polarization conversion optical system.

Abstract: To reduce inconsistencies in an image to be displayed in a projector. At least one of a polarizer on the side of a light incident surface and a polarizer on the side of a light emitting surface is bonded on a sapphire glass plate. The sapphire glass plate may preferably be formed of single-crystal sapphire. In addition, the sapphire glass plate may preferably be held by a holding frame made of metal. The sapphire glass plate and the holding frame made of metal may preferably be bonded by an adhesive agent having superior heat conductivity.

Abstract: In a second lens array 130A of an illumination optical system according to the present invention, the position of curved faces of third minute lenses 132Ab is displaced from the position of curved faces of second minute lenses 132Aa. Such displacement makes the size of a first region W1 on an illuminating area LA, which is irradiated with light transmitted by polarizing separation films 142, substantially equal to the size of a second region W2 on the illuminating area LA, which is irradiated with light reflected by the polarizing separation films 142 and reflection films 144.This arrangement effectively prevents the significant reduction of the illuminating efficiency occurring in a prior art illumination optical system that utilizes a polarization conversion optical system.