Abstract: Transparent light-emitting rod and lamp united to constitute a light source unit are separately placed in an image reading region and a lamp moving region, so that the light-emitting rod can be brought close to a reading platen on which a given objective image sheet to be read is placed, irrespective of the size of the lamp, thereby to lessen the loss of desired light emitted from the light source. The image reading and lamp moving regions are separated by a shielding means so as to effectively remove inadequate heat generated by the light source, thereby to protect the component parts contained in an image scanner from the heat.