A back light unit, in which bright lines produced from point light sources, light emitting diodes, in an oblique direction are removed, so that brightness can be uniformly maintained at a liquid crystal panel. The back light unit includes a prism light guide plate, light emitting diodes provided on one side of the prism light guide plate, and a bright-line dead section provided to the prism light guide plate so as to uniformly scatter light of each light condensing section generated by light emitted from the light emitting diodes, to prevent a spectrum of the light in a specific direction, and to prevent bright lines from being produced.