An upper portion and lower portion of a first lens array may be relatively offset from each other in an x direction. A second lens array is also offset correspondingly to the first lens array. Since an angle at which a partial light beam transmitted through the upper portions of the first and second lens arrays illuminates an area of illumination is different from an angle at which a partial light beam transmitted through the lower portions of the first and second lens arrays illuminates the area of illumination, dark lines generated by these partial light beams appear in different positions on a screen. With this arrangement, the dark lines resulting from the center line of a cross-dichroic prism are made less visible.