A back-light module includes a light-guiding plate and a light source. The light-guiding plate has a lateral inlet surface. The light source is arranged at one side of the lateral inlet surface. The light source has a plurality of light-emitting diodes which are disposed in a line and at interval. A gap is formed between the adjacent light-emitting diodes. The lateral inlet surface dispose a plurality of convex lenses, each of the convex lenses has a convex surface facing to the corresponding gap between the adjacent light-emitting diodes.