Abstract: In a knitting machine in which upon the application of abnormal tension to yarn, the yarn is released from a yarn engaging element and simultaneously the knitting machine is halted. A yarn replacing apparatus is provided comprising at least one vertical motion mechanism for receiving yarn released from a yarn engaging element and moving it upward into reengagement with the yarn engaging element. The vertical motion mechanism further includes a detecting device for detecting an abnormal condition in the yarn, whereby when abnormal tension applied to the yarn has been removed, the vertical motion mechanism continues to operate, whereas when the abnormal tension applied to the yarn has not been removed, the vertical motion mechanism is halted, and the knitting machine automatically again comes into operation only after the reengagement of the released yarn with the yarn engaging element.