PURPOSE: To prevent intrusion of water into the main line from the opening at the forward end of a round tube in a wire harness having a branch applied with the round tube.

CONSTITUTION: Branch wire groups 12A-12E from a main line 11 are applied with round tubes 13 and the terminal of each wire projecting from the opening at the forward end of the round tube 13 is connected with a connector 14. In such a wire harness the branch wire group fixed with a terminal at the forward end thereof is applied with a round tube through the round tube 13 from the terminal fixing side. A thermal fusing means or an ultrasonic fusing means is then applied instantaneously or for a short time to a part of the round tube 13 thus deforming the round tube 13 plastically. Consequently, the round tube 13 is applied tightly to the outer peripheral surface of each wire passed through the tube while filling the gap between the wires thus preventing intrusion of water through the gap between the opening at the forward end of the round tube 13 and the connector 14.