To simplify a process, to reduce the cost, and to provide the complete water-proofing, by aligning the wires at the wiring of the wires on an assembling line, separately conveying the same one by one, and coating the same with a water cut-off agent of specific viscosity.

An alinging jig 12 is installed when the wires are wired on a wiring base 10, when a wire harness is assembled, and a group of wires W is inserted between a pair of wire guide plates 12a, 12b. On the insertion, both sides of the upper openings 12f of the guide plates 12a, 12b are tilted and opened, so that the wires are aligned one by one to be pushed into a conveying passage 12e by pushing the group of wires W, even though the group of wires W is mounted in a lump. Then each wire is fitted into the water cut-off agent in a liquid storing part, so that it is uniformly coated with the water cut-off agent. On this occasion, the viscosity of the water cut-off agent is 1,000-2,000 poise. Thereby the coating process of the water cut-off agent can be performed on the assembling line without performing the same in the other process, thereby the water-proof treatment process can be simplified and performed rapidly.