A lighting unit and a liquid crystal display device which can improve the efficiency of usable light. The lighting unit includes a light source, a light guide plate, and a truncated pyramid located between the light guide plate and the light source. The truncated pyramid has a base, a top smaller than the base, and a slope linking the base and the top. The light source is placed in close contact with the top of the truncated pyramid, and the light guide plate is placed in close contact with the base of the truncated pyramid. Light is propagated from a light emitting part of the light source to the light guide plate without passing through any air layer. Also, an unnecessary light removing structure is provided in the light guide plate near the incidence surface thereof.