A multi-beam photoelectric sensor is disclosed which can be fabricated by selecting the length of a light projectionlight-receiving columnar member and the number and pitches of optical axes in accordance with the width of a hazardous area of an object or the diameter of the minimum object to be detected. The tag comprises a plurality of diffractive elements which are indicative of data carried by the tag. The clearance is loaded with a filler having a low modulus of elasticity, as required.