Lighting device, image-reading device, color-document reading apparatus, image-forming apparatus, projection apparatus

A lighting device, comprising:

• an illumination face that reflects and/or absorbs light, and has-a predetermined length and width, the lighting device configured to apply light onto the illumination face to utilize reflected light from the illumination face;
• and
• a light-source unit including a light-emitting element having a light emitting diode;
• and an optical element that has a light-ray incident opening near a light-ray releasing face of the light-emitting element and a concave-face reflecting unit that has a partially cylindrical shape having a light-ray releasing opening that faces the illumination face, with a cross sectional shape of the concave-face reflecting unit including a quadratic curve or a pseudo quadratic curve (hereinafter, “a quadratic curve”), wherein
• an illumination area derived from light applied from the light-emitting element has a luminance distribution area having a flat portion, with the-flat portion being virtually coincident with the illumination face, the concave-face reflecting unit being constituted by a curve that is located on one side when viewed from the vicinity of an apex of the quadratic curve and a symmetric axis of the quadratic curve.