PURPOSE: To form excellent knotting power in a knotting part positively and easily, by inserting a cushion material into a knotting part void, and tightening up the knotting part, in case of a knotting part forming process.

CONSTITUTION: In case of an ordinary knot A, first a knot 2 is made in a monofilament 1, then a cushion material 5 is inserted into a void part 3, and both ends 1 and 1' are tightened up. And, in case of a loop knot, the end 1' is adjusted to the live string side 1 of the monofilament, producing the knot 2 and a loop 4, and the cushion material 5 is inserted into the void part 3, then both ends 1 and 1' and the loop 4 are tightened up. In case of an 8-shaped knot C, the end 1' is adjusted to the live string side 1, producing an 8-shaped knot 2 and the loop 4, and they are tightened up likewise. In addition, a double 8-shaped knot D is also tightened up in the same manner. Thus, knotting power is improved, and it is useful in the case where fishlines themselves consisting of the plastic monofilament are joined together, or an anchorage such as a fastener ring or the like is joined to a knotting part of the fishline.