An optical member includes a lens array including lens bodies, and transmissive members. The transmissive members are made of a material having a uniform refractive index, and are disposed at positions nearer an object-to-be-read than the corresponding lens bodies are disposed or at positions farther from the object-to-be-read than the corresponding lens bodies are disposed. The transmissive members have a columnar shape extending along the optical axes of the lens bodies, and allow light incident through one end faces to exit through the other end faces. At least either ones of the lens bodies or the transmissive members are arranged with distances therebetween larger than errors in the arrangement of the lens bodies and the transmissive members.