A yarn travelling information acquiring device comprising: a first detecting section adapted to detect a thickness unevenness of a travelling yarn and to output a first yarn thickness unevenness signal; a second detecting section arranged upstream in a yarn travelling direction at a distance from the first detecting section, and adapted to detect the thickness unevenness of the yarn and to output a second yarn thickness unevenness signal; a similarity degree evaluating section adapted to determine a plurality of similarity degrees of the first yarn thickness unevenness signal and the second yarn thickness unevenness signal in accordance with the first yarn thickness unevenness signal acquired within a first time range, and the second yarn thickness unevenness signal acquired within a second time range, the second time range being longer than the first time range; a weighting processing section adapted to perform a weighting processing on each of the plurality of the similarity degrees using a weighting factor and to calculate a plurality of weighted similarity degrees; and a travelling information acquiring section adapted to calculate a time delay between the first yarn thickness unevenness signal and the second yarn thickness unevenness signal in accordance with a maximum weighted similarity degree among the plurality of the weighted similarity degrees, and to acquire travelling information of the yarn in accordance with the distance and the time delay, characterized in that the weighting factor is designated by a weighting curve according to a speed ratio being obtained in accordance with a reference delay amount and a calculated delay amount of the first yarn thickness unevenness signal and the second yarn thickness unevenness signal. a first detecting section adapted to detect a thickness unevenness of a travelling yarn and to output a first yarn thickness unevenness signal; a second detecting section arranged upstream in a yarn travelling direction at a distance from the first detecting section, and adapted to detect the thickness unevenness of the yarn and to output a second yarn thickness unevenness signal; a similarity degree evaluating section adapted to determine a plurality of similarity degrees of the first yarn thickness unevenness signal and the second yarn thickness unevenness signal in accordance with the first yarn thickness unevenness signal acquired within a first time range, and the second yarn thickness unevenness signal acquired within a second time range, the second time range being longer than the first time range; a weighting processing section adapted to perform a weighting processing on each of the plurality of the similarity degrees using a weighting factor and to calculate a plurality of weighted similarity degrees; and a travelling information acquiring section adapted to calculate a time delay between the first yarn thickness unevenness signal and the second yarn thickness unevenness signal in accordance with a maximum weighted similarity degree among the plurality of the weighted similarity degrees, and to acquire travelling information of the yarn in accordance with the distance and the time delay, characterized in that the weighting factor is designated by a weighting curve according to a speed ratio being obtained in accordance with a reference delay amount and a calculated delay amount of the first yarn thickness unevenness signal and the second yarn thickness unevenness signal.