A light source device (1, 301, 401, 501, 601, 801), comprising: a holder having a first horizontal surface and a second horizontal surface and being an integral structure, the second surface being located higher than the first surface; a semiconductor light-emitting device on the first surface; a reflective optical element (20, 525) above the semiconductor light-emitting device, the reflective optical element (20, 525) having a reflective surface (21a, 526a) that inclines with respect to the first surface and configured to reflect emitted light from the semiconductor light-emitting device onto a phosphor element along an optical axis of the reflective surface directed towards the phosphor element, wherein the reflective optical element (20, 525) includes: a holding member on a third surface of the holder, the holding member being opaque; and a reflector element (21, 526) having the reflective surface (21a, 526a) and fixed to a surface of the holding member that faces the semiconductor light-emitting device; the phosphor optical element on the second surface, the phosphor optical element being configured to be irradiated with reflected light from the reflective optical element (20, 525); and a light-transmissive cover above the phosphor optical element, wherein the semiconductor light-emitting device and the phosphor optical element are disposed in a closed space surrounded by the holder, the holding member, and the light-transmissive cover, wherein a surface of the holder opposite the first surface is a first heat-dissipating surface configured to dissipate heat generated at the semiconductor light-emitting device, and a surface of the holder opposite the second surface is a second heat-dissipating surface configured to dissipate heat generated at the phosphor optical element, wherein the first heat-dissipating surface and the second heat-dissipating surface are flush, wherein the holder is an integral heat dissipator, and wherein the light-transmissive cover is a material that is transparent for light radiated by the phosphor optical element; whereby a surface of the light-transmissive cover that faces the phosphor optical element inclines with respect to a fluorescent surface of the phosphor optical element. a holder having a first horizontal surface and a second horizontal surface and being an integral structure, the second surface being located higher than the first surface; a semiconductor light-emitting device on the first surface; a reflective optical element (20, 525) above the semiconductor light-emitting device, the reflective optical element (20, 525) having a reflective surface (21a, 526a) that inclines with respect to the first surface and configured to reflect emitted light from the semiconductor light-emitting device onto a phosphor element along an optical axis of the reflective surface directed towards the phosphor element, wherein the reflective optical element (20, 525) includes: a holding member on a third surface of the holder, the holding member being opaque; and a reflector element (21, 526) having the reflective surface (21a, 526a) and fixed to a surface of the holding member that faces the semiconductor light-emitting device; the phosphor optical element on the second surface, the phosphor optical element being configured to be irradiated with reflected light from the reflective optical element (20, 525); and a holding member on a third surface of the holder, the holding member being opaque; and a reflector element (21, 526) having the reflective surface (21a, 526a) and fixed to a surface of the holding member that faces the semiconductor light-emitting device; the phosphor optical element on the second surface, the phosphor optical element being configured to be irradiated with reflected light from the reflective optical element (20, 525); and a light-transmissive cover above the phosphor optical element, wherein the semiconductor light-emitting device and the phosphor optical element are disposed in a closed space surrounded by the holder, the holding member, and the light-transmissive cover, wherein a surface of the holder opposite the first surface is a first heat-dissipating surface configured to dissipate heat generated at the semiconductor light-emitting device, and a surface of the holder opposite the second surface is a second heat-dissipating surface configured to dissipate heat generated at the phosphor optical element, wherein the first heat-dissipating surface and the second heat-dissipating surface are flush, wherein the holder is an integral heat dissipator, and wherein the light-transmissive cover is a material that is transparent for light radiated by the phosphor optical element; whereby a surface of the light-transmissive cover that faces the phosphor optical element inclines with respect to a fluorescent surface of the phosphor optical element.