the clothes to be placed thereon so that the position of the button is fixed to expose a sewing line referring to fig1 a lower direction in which the holder 12 of the body 10 is placed is referred to as a front direction or surface and an upper direction is referred to as a rear direction or surface in this case the holder 12 of the body 10 includes a straight groove 14 a v shaped groove 15 and a concave groove 16 the straight groove 14 is formed by incising the holder 12 in the longitudinal direction such that the sewing thread of the button b is held while passing through the straight groove 14 the v shaped groove 15 is incised toward an upper side of the straight groove 14 such that the separating arm 51 described later is rested therein the concave groove 16 is formed on a rear surface of the holder 12 in an arc shape to knot the thread t in a figure u201c 8 u201d shape a tension control unit 20 according to the present invention includes tensioners 21 22 and 23 and a thread hook 25 on a passage of the thread t the thread t is provided to the holder 12 from a rear side end through a tensioner 21 positioned upstream a middle tensioner 22 and a tensioner 23 positioned downstream a thread hook 25 is disposed between the tensioners 21 to 23 to maintain the tension necessary when the thread t is wound and knotted the thread hook 25 of the tension control unit 20 has a hole 26 formed adjacent to the tensioner 23 positioned downstream and the tension.