A light source device includes a light source section for supplying a laser beam, a wavelength conversion element for converting a wavelength of the laser beam from the light source section, a temperature measuring section for measuring temperature, a temperature adjusting section for adjusting the temperature of the wavelength conversion element in accordance with a result of the measurement by the temperature measuring section, and a thermal diffusion section for diffusing heat to be conducted to the wavelength conversion element, wherein the thermal diffusion section is provided with a first surface disposed on a side of the wavelength conversion element and a second surface disposed on an opposite side to the first surface, and the temperature measuring section is provided to a part of the thermal diffusion section, which is located on a side of the second surface and has higher thermal conductivity of the thermal diffusion section between the side of the first surface and the side of the second surface than the other part of the thermal diffusion section.