A scanning unit includes a lamp-mounting body having a top surface formed with an elongate opening that is disposed between a pair of parallel first and second grooves. First and second reflective layers are attached respectively over curved groove-defining surfaces of walls defining respectively the first and second grooves. Tubular first and second lamps are mounted respectively in the first and second grooves. An intersecting line of a first plane in which a middle line of the curved groove-defining surface defining the first groove and a first central axis of the first lamp are disposed, and a second plane in which a middle line of the curved groove-defining surface defining the second groove and a second central axis of the second lamp are disposed, is located on a scanning surface, and is disposed directly above the opening.