A backlight unit including a light source and a light guide plate adapted to guide light from the light source to a liquid crystal panel, the light guide plate having a light emission plane to be arranged opposite the liquid crystal panel for emission of light toward the liquid crystal panel, wherein the light source comprises light emitting diodes received in grooves formed in the rear plane of the light guide plate which is opposite the light emission plane of the light guide plate, and the light-emitting diodes are side-emission-type light-emitting diodes so that light emitted from each light emitting diode enters the light guide plate from a light incidence plane at a side of each groove, a predetermined shape to diffuse or disperse light is formed on a lateral side perpendicular to the light emission plane of the light guide plate and/or at an edge portion near the lateral side of the light emission plane,, and wherein the predetermined shape is an optical pattern to diffuse or disperse light which: is formed by a rough plane (101, 103) having minute unevenness, wherein a density of the minute unevenness of the rough plane (101, 103) near light emitting diodes is different from that apart from light emitting diodes in emission direction of light from the light emitting diodes, or is formed by prisms, wherein a pitch between the prisms near light emitting diodes or an angle of the prisms near light emitting diodes is different from that apart from light emitting diodes in emission direction of light from the light emitting diodes, the backlight unit being characterised in that reflection elements are disposed at places to the lateral sides of the light guide plate, inclined so as to spread from the rear of the light guide plate toward the liquid crystal panel, to reflect light emitted from the lateral sides of the light guide plate toward the liquid crystal panel. the light source comprises light emitting diodes received in grooves formed in the rear plane of the light guide plate which is opposite the light emission plane of the light guide plate, and the light-emitting diodes are side-emission-type light-emitting diodes so that light emitted from each light emitting diode enters the light guide plate from a light incidence plane at a side of each groove, a predetermined shape to diffuse or disperse light is formed on a lateral side perpendicular to the light emission plane of the light guide plate and/or at an edge portion near the lateral side of the light emission plane,, and wherein the predetermined shape is an optical pattern to diffuse or disperse light which: is formed by a rough plane (101, 103) having minute unevenness, wherein a density of the minute unevenness of the rough plane (101, 103) near light emitting diodes is different from that apart from light emitting diodes in emission direction of light from the light emitting diodes, or is formed by prisms, wherein a pitch between the prisms near light emitting diodes or an angle of the prisms near light emitting diodes is different from that apart from light emitting diodes in emission direction of light from the light emitting diodes, the backlight unit being characterised in that reflection elements are disposed at places to the lateral sides of the light guide plate, inclined so as to spread from the rear of the light guide plate toward the liquid crystal panel, to reflect light emitted from the lateral sides of the light guide plate toward the liquid crystal panel. is formed by a rough plane (101, 103) having minute unevenness, wherein a density of the minute unevenness of the rough plane (101, 103) near light emitting diodes is different from that apart from light emitting diodes in emission direction of light from the light emitting diodes, or is formed by prisms, wherein a pitch between the prisms near light emitting diodes or an angle of the prisms near light emitting diodes is different from that apart from light emitting diodes in emission direction of light from the light emitting diodes, the backlight unit being characterised in that reflection elements are disposed at places to the lateral sides of the light guide plate, inclined so as to spread from the rear of the light guide plate toward the liquid crystal panel, to reflect light emitted from the lateral sides of the light guide plate toward the liquid crystal panel.