A lighting unit including a plurality of linear or bar-shaped light sources arranged in parallel, a light-guiding plate having a plurality of grooves to accommodate the light sources, a light diffuse reflector provided at either one side of the light-guiding plate, a first light diffuser provided at the side opposite to that which faces the light diffuse reflector of the light-guiding plate, and a light semi-transmitting reflector provided between each light source and the light diffuser. A second light diffuser is located with a clearance at the side opposite to that which faces the light-guiding plate of the first light diffuser.