in addition the projection like needle thread contacts 66 67 are finished to a smooth surface the projection like needle thread contacts 66 and 67 which are formed adjacent to the rotating hook bobbin case holder position bracket 3 in the rotating hook bobbin case holder 60b and bobbin case 63a respectively are located on the rotation direction side of free running with the rotating hook 2 not shown when the loop of the needle thread captured by the hook point not shown of the rotating hook goes through into the rotating hook bobbin case holder 60b or 62 the needle thread contact 66 or 67 temporarily fastens the needle thread to oscillate the rotating hook bobbin case holder in a direction opposite to the rotation direction of the rotating hook 2 by the tension of the needle thread the operation of the fourth embodiment is identical to that of the first embodiment shown in fig2 that is as the rotating hook rotates the loop of the needle thread 50 captured by the hook point 20 of the rotating hook moves sequentially from one position to another and when reaching position 50e the needle thread 50 makes contact with the needle thread contact 66 or 67 caught by the projection and generates pressure force for an extremely short time this causes the rotating hook bobbin case holder 60b or 62 to be instantaneously provided with torque in the opposite rotation direction and the first space s1.