A three-dimensional, 3D, image display apparatus comprising: a directional backlight unit comprising: a light source configured to emit light; a light guide plate comprising: an incident surface on which light emitted by the light source is incident; and an emission surface from which the light incident on the incident surface is emitted; a reflective surface facing the emission surface; and a diffractor configured to diffract light toward a plurality of viewing zones; and a display panel provided to modulate the diffracted light radiated from the directional backlight unit, based on image information, wherein the directional backlight unit further comprises a reflective polarizer provided on the emission surface and configured to transmit a portion of the light as first polarized light having a first polarization direction and reflect another portion of the light as second polarized light having a second polarization direction and being perpendicular to the first polarized light, and wherein the diffractor is configured to diffract the first polarized light transmitted through the reflective polarizer toward a plurality of viewing zones and wherein the display panel comprises only one polarizing plate; and characterized in that the diffractor comprises a plurality of diffractor units, wherein each of the plurality of diffractor units comprises a plurality of sections corresponding to a number of the plurality of viewing zones, wherein each of the plurality of sections comprises a grating unit configured to control an emission direction of light, and wherein each of the grating units comprises a plurality of sub-grating units, and optionally wherein: each of the sub-grating units comprises gratings; and an arrangement direction or an arrangement interval of the gratings comprised in one of the plurality of sub-grating units differs from an arrangement direction or an arrangement interval of the gratings comprised in another of the plurality of sub-grating units, and wherein no polarizing plate is provided on a surface on which light is incident from the directional backlight unit, and wherein light from the light source passes the reflective polarizer, the diffractor and the display panel sequentially. a directional backlight unit comprising: a light source configured to emit light; a light guide plate comprising: an incident surface on which light emitted by the light source is incident; and an emission surface from which the light incident on the incident surface is emitted; a reflective surface facing the emission surface; and a diffractor configured to diffract light toward a plurality of viewing zones; and a light source configured to emit light; a light guide plate comprising: an incident surface on which light emitted by the light source is incident; and an emission surface from which the light incident on the incident surface is emitted; an incident surface on which light emitted by the light source is incident; and an emission surface from which the light incident on the incident surface is emitted; a reflective surface facing the emission surface; and a diffractor configured to diffract light toward a plurality of viewing zones; and a display panel provided to modulate the diffracted light radiated from the directional backlight unit, based on image information, wherein the directional backlight unit further comprises a reflective polarizer provided on the emission surface and configured to transmit a portion of the light as first polarized light having a first polarization direction and reflect another portion of the light as second polarized light having a second polarization direction and being perpendicular to the first polarized light, and wherein the diffractor is configured to diffract the first polarized light transmitted through the reflective polarizer toward a plurality of viewing zones and wherein the display panel comprises only one polarizing plate; and characterized in that the diffractor comprises a plurality of diffractor units, wherein each of the plurality of diffractor units comprises a plurality of sections corresponding to a number of the plurality of viewing zones, wherein each of the plurality of sections comprises a grating unit configured to control an emission direction of light, and wherein each of the grating units comprises a plurality of sub-grating units, and optionally wherein: each of the sub-grating units comprises gratings; and an arrangement direction or an arrangement interval of the gratings comprised in one of the plurality of sub-grating units differs from an arrangement direction or an arrangement interval of the gratings comprised in another of the plurality of sub-grating units, and wherein no polarizing plate is provided on a surface on which light is incident from the directional backlight unit, and wherein light from the light source passes the reflective polarizer, the diffractor and the display panel sequentially.