A detecting structure for a stuffing apparatus includes: a stuffing nozzle having a material discharge port and a photoelectric sensor for detecting a terminating end of a casing loaded on an outer periphery of the stuffing nozzle, wherein the photoelectric sensor is accommodated in a protective case having a transparent portion, and a first air supplying arrangement for supplying air into the protective case is provided on the protective case. Further, the first air supplying arrangement may have an air nozzle which is provided in the protective case and jets air toward an inner surface of the transparent portion. Still further, second air supplying arrangement may be provided for supplying air toward an outer surface of the transparent portion. Furthermore, third air supplying arrangement may be provided for supplying air toward the casing.