To guarantee excellent stitch formation even in the case of thread whose processing is extremely difficult in a method for improving the pull-in of a needle thread loop at the time of forming a lock stitch and a shuttle constituted corresponding to the method.

The upward movement of the needle thread loop is temporarily stopped at least inside the last quadri-sected section of the loop movement of the needle thread loop. The leg part of a slackened needle thread loop moved along the front end face 27 of a bobbin case 19 is made to go over the front end face 27 of the bobbin case 19 and deflected. When the upward movement of the needle thread loop is about to end, the needle thread loop is horizontally directed to bobbin thread guided in an almost vertical direction on a route from the bobbin case 19 to a piercing hole and supplied to the bobbin thread.