In the present invention, the cross-section of a beam from a light-emitting element is shaped, with light-transmission losses reduced. A light-source device (13) for an endoscope is provided with the following: a light-emitting-element part (71) that has a laser diode (LD2) and a light-source module that has a beam-shaping part (73). Said beam-shaping part (73) is a prism-shaped light-guiding rod, and the cross-section thereof perpendicular to an optical axis (A) is hexagonal. A substantially elliptical beam emitted by the laser diode (LD2) is shaped by the beam-shaping part (73) into a substantially circular shape. When a minor-axis component (RS) of the elliptical beam enters the beam-shaping part (73), said minor-axis component (RS) is guided in the direction of the optical axis (A) while undergoing total internal reflection at the interior surface of a side face (73b) of the beam-shaping part (73). As the beam is being thus guided, since minor-axis components (RS) are incident upon sides of the hexagon at non-perpendicular angles, said minor-axis components (RS) are reflected at angles, causing rotation about the optical axis (A). Many of the light rays constituting the beam undergo such rotation, shaping the cross-section of the beam into a substantially circular shape.La présente invention vise à réduire les pertes de transmission de la lumière lors de la mise en forme de la section transversale dun faisceau provenant dun élément électroluminescent. Le dispositif démission de lumière (13) selon linvention destiné à un endoscope comprend : un élément électroluminescent (71) muni dune diode laser (LD2) et un module démission de lumière muni dun élément de mise en forme de faisceau (73). Ledit élément de mise en forme de faisceau (73) est une barre guide dondes lumineuses en forme de prisme, dont la section transversale est hexagonale perpendiculairement à un axe (A). Un faisceau sensiblement elliptique émis par la diode laser (LD2) est mis par lélément de mise
