The utility model provides a photoelectric sensor enabling a detection scope of a detected target to be smaller than a regulated size; the photoelectric sensor comprises a light source, a lens, a photoreceptor, a first diaphragm and a second diaphragm; the light source is used for sending detection light; the lens focuses the light emitted from the light source to a detection area; the photoreceptor receives the through light passing the detection area; the first and second diaphragms are arranged between the light source and the lens; the first diaphragm is arranged in a position more closer to the light source when compared with the second diaphragm; an opening size of a cross section comprising an optical axis of the lens of the first diaphragm is bigger than that of the second diaphragm; the effective size of the light source is bigger than the opening size of the first diaphragm; the effective size of the lens is bigger than that of the light source.