A display device comprising: a light source arranged to emit light in a predetermined wavelength range; an optical sheet into which light is incident from the light source, the optical sheet including a light conversion sheet that comprises a host layer and a plurality first light conversion particles dispersed therein to convert the wavelength of light emitted by the light source; a display panel disposed on the optical sheet and including an effective display region and a non-effective display region around the effective display region; the display device being characterized by further comprising: a light conversion/light-blocking sheet disposed between the display panel and the optical sheet so as to extend along the outer peripheral portions of the optical sheet and so as to correspond to the non-effective display region, the light-conversion/light- blocking sheet being arranged to block light incident on its display panel side and to reflect light on its opposite side leaked from the light source to the periphery of the optical sheet and to convert the wavelength of said leaked light; wherein the light-conversion/light-blocking sheet includes: a light blocking part disposed adjacent to the display panel; and a wavelength conversion part disposed on the lower surface of the light blocking part adjacent to the optical sheet, wherein the light blocking part includes a reflective surface in direct contact with the wavelength conversion part; and wherein the wavelength conversion part includes a host layer, and a plurality of second light conversion particles dispersed therein. a light source arranged to emit light in a predetermined wavelength range; an optical sheet into which light is incident from the light source, the optical sheet including a light conversion sheet that comprises a host layer and a plurality first light conversion particles dispersed therein to convert the wavelength of light emitted by the light source; a display panel disposed on the optical sheet and including an effective display region and a non-effective display region around the effective display region; the display device being characterized by further comprising: a light conversion/light-blocking sheet disposed between the display panel and the optical sheet so as to extend along the outer peripheral portions of the optical sheet and so as to correspond to the non-effective display region, the light-conversion/light- blocking sheet being arranged to block light incident on its display panel side and to reflect light on its opposite side leaked from the light source to the periphery of the optical sheet and to convert the wavelength of said leaked light; wherein the light-conversion/light-blocking sheet includes: a light blocking part disposed adjacent to the display panel; and a wavelength conversion part disposed on the lower surface of the light blocking part adjacent to the optical sheet, wherein the light blocking part includes a reflective surface in direct contact with the wavelength conversion part; and wherein the wavelength conversion part includes a host layer, and a plurality of second light conversion particles dispersed therein. a light conversion/light-blocking sheet disposed between the display panel and the optical sheet so as to extend along the outer peripheral portions of the optical sheet and so as to correspond to the non-effective display region, the light-conversion/light- blocking sheet being arranged to block light incident on its display panel side and to reflect light on its opposite side leaked from the light source to the periphery of the optical sheet and to convert the wavelength of said leaked light; wherein the light-conversion/light-blocking sheet includes: a light blocking part disposed adjacent to the display panel; and a wavelength conversion part disposed on the lower surface of the light blocking part adjacent to the optical sheet, wherein the light blocking part includes a reflective surface in direct contact with the wavelength conversion part; and wherein the wavelength conversion part includes a host layer, and a plurality of second light conversion particles dispersed therein. a light blocking part disposed adjacent to the display panel; and a wavelength conversion part disposed on the lower surface of the light blocking part adjacent to the optical sheet, wherein the light blocking part includes a reflective surface in direct contact with the wavelength conversion part; and wherein the wavelength conversion part includes a host layer, and a plurality of second light conversion particles dispersed therein.