The weft yarn handling apparatus for a jet looms includes means (8a) for unwinding the weft from a weft supply cheese (3). The length of the unwound weft yarn (Y) is measured and the yarn is stored on a drum (8b) of the measuring and storing device (8) The weft (Y) thus measured and reserved is then transferred to the main nozzle (13) of an air jet loom and then inserted through the shed by fluid injected from the main picking nozzle (13). On the downtream side of the weft measuring and storage device (8) there is a nozzle block arrangement (15; 12, 8a, 15a, 15b, 16) for transferring weft yarn from the measuring and storage device (8) to the main nozzle 13 and in addition means (40) for retaining weft yarn in the case of a weft yarn break. The nozzle block further includes means (22) for cutting the weft (Y) at a predetermined position while said part of the weft (Y) is being retained by said retaining means (40). One cut end of weft yarn (Y) is blown or sucked to a trash box (19) and the other end is guided to the region of suction adjacent to the inlet of weft injection main nozzle (13). The arrangement is operated automatically by a control C, that starts operating when a weft yarn break is detected that required threading of the main nozzle (13). The arrangment provides for a non complicated, fast threading of the main nozzle (13) and low failure rate.