To prevent yarn from striking the side wall of the clamp cover of a clamp so as to injure at being caught by providing the clamp cover on a clamp means, and forming a cutout part on the yarn suction side part of the clamp cover.

A pressing plate 10 is rotationally moved to a block 3 against the elastic force of a spring 6 by a clamp plate 5 together with a clamp cover 9, and hence a clamper is opened. At this time, by a cutout 13 formed on the side wall 9a on the yarn suction side of the clamp cover 9, yarn on the feed bobbin side suckingly held with a yarn suckingly holding means is surely faced to the opening of the clamper, namely, between the extreme end face of the block 3 of a clamp member 2 and the pressing plate 10 of the clamp plate 5, without striking the side wall 9a of the clamp cover 9, and it is sucked into the hole 3a of the lock 3 of the clamper.