Image reading device

In an image reading device in which an image of an object is applied through an optical system, having at least a reflective optical element and an image forming lens defining therebetween an optical axis, said optical axis lying in a first plane, to a photoelectric conversion means, and said photoelectric conversion means produces an electrical signal representing the image of said object, the improvement comprising:

• said optical system and said photoelectric conversion means being fixedly secured to a single supporting frame in a predetermined positional relationship, and said supporting frame being detachably mounted on a mounting surface of an image reading device body;
• and
• wherein said supporting frame further comprises a light-shielding plate having a first end attached to said frame and a free second end with an arcuate edge extending toward and being proximate to said optical axis, said arcuate edge of said plate being closest to said optical axis at a central portion of said edge and gradually curving away from said optical axis towards both ends of said edge, said plate being disposed between said image forming lens and said reflective optical element whereby quantities of light are blocked more at said central portion than at said end portions and said quantity of light at said photoelectric conversion means is made substantially uniform.