PURPOSE: When the breakage of a filament or the loss of cocoon has been found by a knot-removing operator, the operator indicates the occurrence of the trouble before moving to the next spot, and a mending and supplying specialist moves to the spot having the indication and carries out mending of the trouble.

CONSTITUTION: When the breakage of a filament or the loss of cocoon takes place, a knot-removing operator operates the reciprocally movable operation rod 3 along the directions of the arrows to make or break the switch 2. The number of the troubled frame and the position (A, B, C or D) of trouble are displayed on the displaying board 4 by this procedure. A mending and cocoon-supplying specialist moves to the position displayed on the board 4, and mends the trouble. The whole process can be carried out by unskilled workers except for a small number of specialists.