To provide a light source device or the like which reduces the generation of speckle noise by emission of coherent light and fluorescence, and enables the emission of the fluorescence with high efficiency.
The light source device includes: a light source 2 which emits the coherent light; and a fluorescence generating element 3 which includes a fluorescence molecular layer 13 to generate the fluorescence. The fluorescence generating element 3 includes a first mirror 11 and a second mirror 12, which have the fluorescence molecular layer 13 between them and are opposed to each other. The first mirror 11 transmits a part of the coherent light and the fluorescence therethrough and emits them from the fluorescence generating element 3, and light other than the light transmitting through the first mirror 11 out of the coherent light is reflected and propagated between the first mirror 11 and the second mirror 12, while the second mirror 12 reflects the fluorescence and the coherent light toward the first mirror 11. Reflection characteristics of the first mirror 11 are set so that reflectance of the coherent light is enhanced as it gets closer to an incident position of the coherent light from the light source 2 to the fluorescence generating element 3.