To provide a method and an apparatus for monitoring a piecing part in a spinning machine which method can perform simple adequate assignment considering the piecing part and a measuring time or a measured value, and which method can perform accurate classification of the lengths of thickness defect.

The apparatus for monitoring a piecing part in a spinning machine has the following structure: the spinning machine is equipped with a number of spinning stations (1); an automatic piecing apparatus (2) having a piecing unit capable of controlling a piecing speed can be attached on a spinning station; a yarn-monitoring apparatus (6) for monitoring yarn quality is placed on the spinning station (1) or the automatic piecing apparatus (2) ; in a piecing monitoring apparatus of the spinning machine, the automatic piecing apparatus (2) and a yarn-monitoring apparatus (6) are connected to each other via an information-transmitting apparatus; and thereby the piecing parameters of the automatic piecing apparatus (2) can be transmitted to the yarn-monitoring apparatus (6) via the information-transmitting apparatus.