A contact image sensor unit includes: a light source (10) illuminating an original; a rod-like light guide (11) guiding light from the light source to the original; an imaging element (12) forming reflected light from the original on a plurality of photoelectric conversion elements; a sensor substrate (14) on which the plurality of photoelectric conversion elements are mounted; a frame (15) to which they are attached and which has a positioning part (200) for attaching the light guide (11) thereto; and a supporting member (16) which attachably/detachably supports the light guide (11) and is attachably/detachably attached to the positioning part (200). Since the light guide (11) can be attached to the frame (15) without using an adhesive, the deformation of the light guide (11), the warpage of the contact image sensor unit and so on can be prevented.