To provide a weft cramping auxiliary device cramping a tip part of the weft attained to a reverse side of yarn feeding with a selvage or a catch cord and preventing generation of loosening of the weft in a fluid jetting loom.

This weft cramping auxiliary device is located at a reverse side of a yarn feeding of a fluid jet loom and at least one of selvages M and a catch cord C is closed earlier than warp T and a closing controlling part material which inhibits a closing of the yarn in being the shedding WO of the earlier closed than the warp T in at least a finishing period of weft inserting and transferable to a waiting position outside of the shedding WO just after finishing of the weft inserting is included in the device.