To provide a light source device capable of effectively extracting light having a small etendue, while enhancing the utilization efficiency of light.

The light source device is equipped with an LED 2 emitting light a first λ1 wavelength; a wavelength conversion element 3, changing the first λ1 wavelength light into light of a second λ2 wavelength; and a light guide body 4 which leads the second λ2 wavelength light to an emission surface 4a, while propagating it inside the body. The wavelength conversion element 3 includes a member 5, containing a phosphor emitting the second λ2 wavelength light by being excited by the first λ1 wavelength light; a first functional film 6 which is arranged on one surface of the member 5, transmitting the first λ1 wavelength light and also reflecting the second λ2 wavelength light; and a second functional film 7 which is arranged on the other surface of the member 5, transmitting the second λ2 wavelength light and also reflecting the first λ1 wavelength light. The LED 2 is arranged in contact with the first functional film 6 of the wavelength conversion element 3, and the light guide body 4 is arranged in contact with the second functional film 7 of the wavelength conversion element 3.