Provided is a back light unit comprising a plurality of LED light source formed on a printed circuit board and a resin layer which is laminated on the LED light source and forwardly induces diffusion of the emitted light wherein the resin layer is made of synthetic resin comprising an oligomer. According to the present invention, an essential light guide plate for a general back light unit configuration is removed and a resin layer mainly consisting of an oligomer is used to guide the light source, and thereby decreasing the number of the light source, minimizing luminance variation when the unit is lighted at a high temperature and kept it for a predetermined time period, and implementing excellent heat-resistant property and optical property.