A light source device includes a light source emitting first light in a first wavelength band, a light guide section guiding partial light of the first light, a wavelength conversion section including a phosphor, which other partial light of the first light, and which converts the other partial light into second light in a second wavelength band. A light guide section first side surface and a wavelength conversion section second side surface are opposed. The first side surface has a diffraction grating. The partial light enters the light guide section from the first side surface via the diffraction grating. The other partial light enters the wavelength conversion section from the second side surface. The partial and second lights are emitted in one of a normal direction of the first end surface of the light guide section and a normal direction of the third end surface of the wavelength conversion section.