The present invention relates to an apparatus having a light source for a transparent sheet of a scanner that includes a lamp, a reflective plate, a spreading plate and a protective plate. The light rays emitted by the lamp are used to scan a transparent sheet, the reflective plate in the arc shape reflects the light rays onto the scanning platform and there is an aperture on the predetermined position of the reflective plate to decrease the illumination for distributing uniformly the light rays. Besides, the spreading plate has a plurality of perforations to advance the light rays distributed uniformly. The protective plate made of the material pervious to light protects the components of this invention. As those described above, there are many advantages for the present invention, such as the structure is simple, the cost is low, and is much practical and can highly improve the performance of a scanner for a transparent sheet.