Image Forming Optical Element and Image Reading Device

An image forming optical element comprising:

• an image forming optical system having a lens array formed of a plurality of lenses that are arranged in line with their light axes being parallel to each other so that an incident optical image from one side of the lens array forms an image on the other side of the lens array;
• a first light shielding member disposed on one side of the image forming optical system and having a plurality of through holes that are arranged in line in the same direction as the lens arrangement direction of the image forming optical system so that light passes through the through holes to be incident on the image forming optical system;
• and
• a second light shielding member disposed on the other side of the image forming optical system and having a plurality of through holes that are arranged in line in the same direction as the lens arrangement direction of the image forming optical system so that outgoing light from the other side of the image forming optical system passes through the through holes, wherein
• the plurality of through holes are decreasingly tapered through holes and increasingly tapered through holes that are alternatively arranged in the same direction as the lens arrangement direction in each of the first light shielding member and the second light shielding member, each decreasingly tapered through hole has a cross sectional area at the upstream opening end which is larger than a cross sectional area at the downstream opening end in a traveling direction of the light that travels from one side to the other side of the image forming optical system, while each increasingly tapered through hole has a cross sectional area at the upstream opening end which is smaller than a cross sectional area at the downstream opening end in the traveling direction of the light, and
• center axes of the decreasingly tapered through holes in the first light shielding member are coincident with center axes of the decreasingly tapered through holes in the second light shielding member, while center axes of the increasingly tapered through holes in the first light shielding member are coincident with center axes of the increasingly tapered through holes of the second light shielding member.