A document scanner with a light focusing device downward formed on a document support panel is disclosed. The document scanner is provided with a chassis including a light source and an image sensing device. A scanning window made of light-transmitting material is formed in an area of the document support panel. A driving roller is arranged in a document feeder for driving a document to be scanned through the scanning window. Light emitted from the light source transmits through the scanning window toward the document and is reflected by the document toward the image sensing device. The document support panel forms a convex projection on a bottom surface thereof. The projection confronts the light source for focusing the light onto the document. Preferably, the projection includes an extended section from the bottom surface of the document support panel and forming a convex end surface confronting the light source. A light collecting rim is further downward formed on the document support panel and around the extended section in a direction toward the light source.