the thermoplastic resin 3 is heated to be melted when the work is made in a state where the ends 11 and 12 of the rubbery core inserted braid 1 are pinched with the pinching tool 4 or between the opening and closing pieces 41 and 41 excellent workability is exhibited and safety is kept when the mold 2 is closed the fluffs of the covering braid moiety of the rubbery core inserted braid 1 should not be sandwiched between the partitioning faces of the mold 2 if the fluffs of the covering braid 80 are sandwiched in a large amount between the portioning faces of the mold 2 the mold 2 is not completely closed so that the melted resin remains as a burr or flash this invalidates the commercial value of the product thus the fluffs of the covering braid 80 should not be sandwiched in a state where the ends 11 and 12 of the rubbery core inserted braid 1 are pushed against each other to approach each other the thermoplastic resin 3 is melted therefore the melted resin is certainly filled into the gap between the ends 11 and 12 to penetrate into the ends 11 and 12 of the rubbery core inserted braid 1 in this way the penetration of the melted resin into the ends 11 and 12 is forcibly conducted so that the strength of the end jointed region can be made high the gap between the ends 11 and 12 of the rubbery core inserted braid 1 is surrounded by a circumferential wall 25 a of the through hole 25 in the mold 2 thus the melted resin is.