Provided is a directional backlight unit. The directional backlight unit includes a source light unit configured to generate dot source light, a linear source light generator configured to separate a plurality of source lights, which are output in a direction vertical to a line type output surface, from the dot source light according to different grating periods and generate the separated plurality of source lights as linear source lights, and a light guide panel configured to output backlight, which has a form of flat source lights and includes the plurality of source lights, in a direction vertical to a plate type output surface according to the different grating periods. The linear source light generator includes an incident surface on which the dot source light is incident and the line type output surface on which a plurality of grating patterns having the different grating periods are provided.