Abstract: An optical fiber attaching structure in a photoelectric switch comprises: an optical fiber supporting member (12) made of an elastic material which is attached to one side portion of a casing (20) of a photoelectric switch and formed with through holes (13, 14) for allowing optical fibers (32, 33) to pass and notches (13a, 13b, 14a, 14b, 14c, 14d, 14e) which are extended from peripheries of the through holes toward the outside in a radial direction; a fastening frame (16) which has a space enough to enclose the optical fiber supporting member and in which openings (17, 18) for allowing the optical fibers to pass are formed at the positions corresponding to the through holes of the optical fiber supporting enclosed in the enclosing space and a screw hole (19) is formed in another plane which is perpendicular to a plane in which the openings are formed; and a pressing screw (31) for fixing the optical fibers which are pierced into the through holes to the optical fiber supporting member by pressing a part of th