There is provided such a shape of a light-guiding body that can guide light emitted from a LED while reflecting such light under conditions which satisfy total reflection as much as possible within the light-guiding body, to thereby improve the light intensity on the surface of a document in the shorter axial direction (i.e., the sub-scanning direction), and also, the light-guiding body has such an optimized shape of a light-incoming face that makes it possible to control the angle of light fluxes in the longer axial direction (i.e., the main scanning direction) to thereby illuminate the surface of the document with light having an uniform intensity distribution. Further, a reflecting member is provided at a position opposite the light outgoing face of the light-guiding body so as to improve the efficiency of illuminating an objective image-reading region on the surface of the document.