In a device of the present invention for allowing signal light to enter a light guide body using an optical fiber, a light guide body, which is constituted by dispersing particles for scattering the signal light in an optical medium, is selected as a light guide path which requires an area where a light diffusing function is performed just after incidence of the signal light. An optical connecting material intervenes between one end of the optical fiber from which the signal light is output and opposed one end surface of a particle dispersing light guide body and a desired diffusing function is obtained.