To improve workability in passing a grommet with a resin inner attached to a wire harness through a passing hole on a car body side.

In routing work of a wire harness, a resin case 21 is covered from a tip end on a door side of the wire harness to the grommet 13, and attaching parts 17, 18 on both ends of the grommet are twisted and tilted so as to sequentially passing through the passing hole on the car body side having an elliptical shape. The resin case is removed when the grommet is positioned in a space between the car body and the door, and a part of the wire harness on a door side is passed through the passing hole on the door side. Then the attaching part on the door side is thrust in the passing hole on the door side and is locked by the resin inner, and the attaching part on the car body side is thrust in the passing hole on the car body side and is locked by the resin inner.