A light source device includes a light source configured to emit excitation light, a phosphor which the excitation light enters, the phosphor being configured to emit fluorescence different in wavelength from the excitation light, a plurality of first nanoantennas provided to the phosphor, and a plurality of second nanoantennas provided to the phosphor. Each of the first nanoantennas is formed of metal. Each of the second nanoantennas is formed of a material higher in melting point than the metal. An arrangement area of the plurality of second nanoantennas overlaps an irradiation area with the excitation light in a plan view viewed from a normal direction of the phosphor. An electric field enhancement of the fluorescence is achieved by each of the first nanoantennas and each of the second nanoantennas.