A back light unit using a laser diode is provided to improve optical efficiency by scattering the light with large linearity from the laser diode through a scattering pattern. A light guide plate(30) includes a light inputting unit(30a) of a side and a light outputting unit(30b) of an upper side or a lower side. A laser diode(10) emits the light to the light inputting unit. The light inputting unit includes a scattering pattern(32). The scattering pattern scatters the light of the laser diode and discharges the light. A fluorescent material(20) is formed on the light emitting surface of the laser diode. The laser diode is a blue laser diode.
