screw 21 at its one end to a base 20 supported to a machine frame and is mounted at its other end to a support plate 22 which is rigidly secured to the base 20 the thread tension shaft 23 has mounted thereon thread tension discs 13 13a for holding an upper thread 12 and a presser body 16 for uniformly pressing a thread tension disc numeral 19 denotes a regulating or adjusting bolt having a brim or edge contacting the thread tension spring 15 and mounted on the thread tension shaft 23 the support plate 22 is secured with a pin 25 at a center thereof between the thread tension shaft 23 and the base 20 and is provided with a dial 10 rotated about the pin 25 a thrust is formed by a brimmed screw 26 fitted in a screw hole formed in the pin 25 numeral 18 is a middle plate which holds a pin 14 engaged in a cam groove 17 formed in the dial 10 and extending through an oblong hole formed in the support plate 22 the middle plate 18 is defined with a projection 35 meshing with the adjusting bolt 19 projection 35 extends transversely of the thread tension shaft 23 and engages an indicating lever 30 for indicating the thread tension an indicating needle 27 shown in fig3 is rotated clockwise by a spring 28 about a stepped screw 29 on the indicating lever 30 a.