A light-emitting device comprising: a substrate; a light emitting diode disposed on the substrate; a wavelength conversion unit that is disposed to face the light emitting diode in a z-direction and includes a transparent member and a wavelength conversion member comprising a quantum dot, the wavelength conversion member converting first wavelength light from the light emitting diode to second wavelength light, wherein the wavelength conversion unit includes a front surface (30S1) and a back surface (30S2), the transparent member containing therein the wavelength conversion member; and a wall member that is provided on the substrate and surrounds the light emitting diode in a x-y-plane that is orthogonal to the z-direction, wherein the wall member includes an inner wall surface that reflects the first wavelength light derived from the light emitting diode, wherein the inner wall surface is inclined to be away from the light emitting diode, as the inner wall surface goes toward the wavelength conversion unit from the substrate, a region occupied by the wavelength conversion member being wider than a region (R21U) surrounded by the wall member, and entirely overlapping with the region (R21U) surrounded by the wall member in the z-direction, wherein the wall member is directly or indirectly in contact with the back surface (30S2) of the wavelength conversion unit and holds the wavelength conversion unit, wherein a constituent material of the wall member includes a thermally-conductive material having higher thermal conductivity than the thermal conductivity of the wavelength conversion unit, characterized in that a wavelength selective reflection layer is provided on a light-incidence surface of the wavelength conversion unit to remove light components of unnecessary wavelength regions and select light components of desired wavelength regions, and in that an air layer is provided between the light source and the wavelength conversion unit. a substrate; a light emitting diode disposed on the substrate; a wavelength conversion unit that is disposed to face the light emitting diode in a z-direction and includes a transparent member and a wavelength conversion member comprising a quantum dot, the wavelength conversion member converting first wavelength light from the light emitting diode to second wavelength light, wherein the wavelength conversion unit includes a front surface (30S1) and a back surface (30S2), the transparent member containing therein the wavelength conversion member; and a wall member that is provided on the substrate and surrounds the light emitting diode in a x-y-plane that is orthogonal to the z-direction, wherein the wall member includes an inner wall surface that reflects the first wavelength light derived from the light emitting diode, wherein the inner wall surface is inclined to be away from the light emitting diode, as the inner wall surface goes toward the wavelength conversion unit from the substrate, a region occupied by the wavelength conversion member being wider than a region (R21U) surrounded by the wall member, and entirely overlapping with the region (R21U) surrounded by the wall member in the z-direction, wherein the wall member is directly or indirectly in contact with the back surface (30S2) of the wavelength conversion unit and holds the wavelength conversion unit, wherein a constituent material of the wall member includes a thermally-conductive material having higher thermal conductivity than the thermal conductivity of the wavelength conversion unit, characterized in that a wavelength selective reflection layer is provided on a light-incidence surface of the wavelength conversion unit to remove light components of unnecessary wavelength regions and select light components of desired wavelength regions, and in that an air layer is provided between the light source and the wavelength conversion unit.