A light source apparatus includes an optical illumination unit that converts optical characteristics of primary light emitted from a light source unit and emits secondary light different from the primary light; and an adapter unit that outwardly emits illumination light generated based on the secondary light emitted from the optical illumination unit and that is attachable to/detachable from the optical illumination unit. A radiation angle control member converts a traveling direction of the secondary light so that the secondary light allowed to emit from a light conversion member toward the radiation angle control member in the secondary light allowed to emit from the light conversion member travels toward the adapter unit through the secondary light emit portion.