PURPOSE: To eliminate the need for the aid of manual labor at the time of threading by freely rotatably mounting a pair of bridle rolls to a mounting base and rotating the bridle rolls in a released state.

CONSTITUTION: A mounting base 5 is rotated to position the bridle rolls 8, 9 to a place where there is no need for winding a sheet 1 around the rolls at the time of threading. The sheet 1 is automatically passed in a linear path and there is no need for the aid of manual labor at the time of threading. A driving sprocket 4 is then rotated to rotate the mounting base 5 in a clockwise direction A in Fig. until the sheet 1 is wound around the bridle rolls 8, 9 if the device is going to be acted as the bridle rolls. The winding angle is arbitrarily settable and the setting of this angle at about ≥180° in average per roll is possible as well. The mounting base 5 is fixed by a clamping device 7 after the angle is set.