A configuration is adopted in which an image sensor unit includes: a sensor substrate on which a plurality of photoelectric conversion elements are mounted; a light source that includes light-emitting elements and is for illuminating a document; a light guide that guides light from the light source from one end face in a longitudinal direction and linearly illuminates the document; a rod lens array imaging reflected light from the document on the sensor substrate; and a frame attaching each of these, and in which the frame detachably includes a spacer provided in proximity to the light source, and the spacer includes a light shield roof elongated so as to cover the light source and the end of the light guide.