Abstract: A positioning device (1) wherein a structure (2), equipped with at least a crossing through hole “delimited” by an annular cavity (2), and an adhering annular member (4) made of flexible and soft material, with an inner diameter smaller than the one of the through hole and an outer diameter suitable for allowing it to house within the annular cavity (3) in the above-mentioned structure (2), are combined, as well as the method consisting in the positioning of one or more positioning devices (1) onto the elongated structure (6) therewith the necklace, or other decorative member, is manufactured and in the application of one or more sliding decorative members onto the device(s) (1) and/or in the section or sections of the elongated structure (6) included between pairs of the positioning devices (1).