PURPOSE: To facilitate the extension operation of gut by pulling the gut clamped in a clamper by horizontally moving a supporting base by rotational operation of a handle and acting braking force on this supporting base when prescribed tension is attained and a supporting rod is rotated by overcoming the force of a spring.

CONSTITUTION: The handle 8 formed integrally with a disk 6 for braking is supported on a sliding frame 3 mounted freely movably via turning rings 4, 5 on the supporting base 1 and a pinion 9 meshing with a rack 2 atop the supporting base 1 is fixed to a revolving shaft 7 thereof. The supporting rod 10 mounted with the gut clamper 13 is pivotally fitted 11 to the sliding frame 3. A spring case 20 is moved by overcoming the force of the coil spring 27 by turning of the supporting rod 10 to screw a threaded nut 24 onto a threaded rod 22 inserted into this case 20. Further, a control lever 28 to be turned by turning of the rod 10 is pivotally fitted 29 to the sliding frame 3 and braking elements 33, 34 disengaged by turning of a brake lever 28 are brought into pressurized contact with a disk 6 for braking.