A beam light source of an image display device which displays an image on a screen by scanning an optical beam in a two-dimensional direction in which the beam light source includes a light source that emits a diffuse light modulated according to an image signal, and an optical element that shapes the light emitted from the light source to the optical beam. The optical beam has an elliptically shaped beam spot on the screen in which a major axis of the beam spot is substantially perpendicular to a scanning direction. A horizontal spot size of the optical beam on an exit surface of the optical element is at least or equal to a horizontal spot size of the optical beam on the screen, and the horizontal spot size of the optical beam on the screen is no greater than a horizontal pixel pitch displayed on the screen.