An image reading apparatus (A1) is provided with a pair of light source devices (3), a light introducing member (4), first and second reflectors (7A, 7B), a plurality of light receiving elements (5) and a case (1). The image reading apparatus (A1) comprises first fitting means (71) for positioning the first reflector (7A) and the case (1) by inserting the first reflector (7A) along an insertion direction (z) with respect to the case (1), second fitting means (72) for positioning the light introducing member (4) and the case (1) by inserting the light introducing member (4) along the insertion direction (z) with respect to the case (1), and third fitting means (73) for positioning the second reflector (7B) and the case (1) by inserting the second reflector (7B) along the insertion direction (z) with respect to the case (1).