An optical wavelength-converting device for converting a first waveband light, comprising: a substrate; a phosphor layer disposed on the substrate for converting the first waveband light into a second waveband light; and a composite reflection layer comprising: a first reflection layer disposed between the substrate and the phosphor layer and adjacent to the substrate for reflecting the second waveband light, wherein the first reflection layer is a metallic reflection layer; and a second reflection layer disposed between the first reflection layer and the phosphor layer for adjusting the reflection spectrum of the first reflection layer, wherein the second reflection layer comprises a dielectric multilayer film and the stacks of layers of the dielectric multilayer film are at least three, so that the reflection rate of the composite reflection layer for wavelengths between 400 nm and 700 nm at an angle of incidence of 60° is above 80%, and wherein the second waveband light is reflected by the first reflection layer and the second reflection layer, such that the second waveband light is transmitted through the phosphor layer so as to be outputted in a direction opposite to the first waveband light. a substrate; a phosphor layer disposed on the substrate for converting the first waveband light into a second waveband light; and a composite reflection layer comprising: a first reflection layer disposed between the substrate and the phosphor layer and adjacent to the substrate for reflecting the second waveband light, wherein the first reflection layer is a metallic reflection layer; and a second reflection layer disposed between the first reflection layer and the phosphor layer for adjusting the reflection spectrum of the first reflection layer, wherein the second reflection layer comprises a dielectric multilayer film and the stacks of layers of the dielectric multilayer film are at least three, so that the reflection rate of the composite reflection layer for wavelengths between 400 nm and 700 nm at an angle of incidence of 60° is above 80%, and wherein the second waveband light is reflected by the first reflection layer and the second reflection layer, such that the second waveband light is transmitted through the phosphor layer so as to be outputted in a direction opposite to the first waveband light. a first reflection layer disposed between the substrate and the phosphor layer and adjacent to the substrate for reflecting the second waveband light, wherein the first reflection layer is a metallic reflection layer; and a second reflection layer disposed between the first reflection layer and the phosphor layer for adjusting the reflection spectrum of the first reflection layer, wherein the second reflection layer comprises a dielectric multilayer film and the stacks of layers of the dielectric multilayer film are at least three, so that the reflection rate of the composite reflection layer for wavelengths between 400 nm and 700 nm at an angle of incidence of 60° is above 80%, and wherein the second waveband light is reflected by the first reflection layer and the second reflection layer, such that the second waveband light is transmitted through the phosphor layer so as to be outputted in a direction opposite to the first waveband light.