needle thread s1 controlled by the thread clamper 18 of this invention indicated by continuous lines and thread tension of the needle thread k controlled by a conventional thread tension regulator indicated by short dashed lines fig2 b is a motion diagram showing vertical movement of the needle 12a of the sewing machine shown in fig1 b the top end point c the bottom end point and horizontal movement of the looper 4 b the left end point c the right end point fig2 c is a graph showing the total amount of needle thread supplied in one stitch the axis supplied to the sewing area 9 with ordinate d the needle thread s1 of the present invention being indicated by continuous lines and the needle thread k of a conventional example being indicated by short dashed lines as shown in fig2 a b the thread tension of the needle thread k controlled by the conventional thread tension regulator begins to rise when the rotating angle of the main shaft is 90 u00b0 reaches a peak at around 130 u00b0 falls gradually after that rises again around 250 u00b0 and reaches another peak at around 360 u00b0 0 u00b0 responding to the two peaks of the tension the needle thread k is pulled out of the thread supply source.