Provided is a directional backlight unit that enables a three-dimensional (3D) image to be viewed at various viewing angles. The directional backlight unit includes a light source configured to emit light, a first reflector configured to reflect light emitted from the light source, a second reflector configured to additionally reflect the light reflected by the first reflector, a light guide plate configured to accommodate the light reflected by the first reflector or the second reflector and output the light to an outside, and an angle adjustor configured to rotate the first reflector or the second reflector to a reflective angle. The angle adjustor rotates the first reflector or the second reflector to change an incident angle of the light incident on the light guide plate and a refractive angle of the light output to the outside.