A light diffusing element diffuses light output from an output facet of an optical fiber that enters the light diffusing element at a first end and outputting the diffused light from a second end. The light diffusing element is equipped with a semireflective surface for reflecting a portion of the light, provided at a predetermined portion of the light diffusing element corresponding to the core of the output facet. The semireflective surface intersects at least with the optical axis of the optical fiber. Thereby, propagation of light in directions away from the optical axis of the optical fiber can be promoted during the step of reflecting the portion of the light that enters the light diffusing element.
