A light source device includes a primary light source that emits primary light, a light guide that guides the primary light, an optical conversion unit that converts the primary light emitted from the light guide and having a first light distribution angle into secondary light having a second light distribution angle and emits the secondary light, and a light distribution adjustment unit that adjusts the secondary light to illumination light having a third light distribution angle and emits the illumination light. The light distribution adjustment unit and the optical conversion unit slide each other. The light distribution adjustment unit allows a light distribution adjustment amount for adjusting the second light distribution angle of the secondary light to adjust to the third light distribution angle of the illumination light.
