To perform water cut-off of a wire harness without being limited in a fastening region by a grommet.

A plurality of electric wires 12 are bundled, the plurality of the bundled electric wires 12 are covered with sealing cover materials 30 at two places with an interval therebetween along the longitudinal direction, and a sealant 50 is supplied to a portion P1 between two places covered with the sealing cover materials 30 out of the plurality of the electric wires 12. Furthermore, an atmospheric pressure difference is generated between the portion P1 between two places covered with the sealing cover material out of the plurality of the electric wires 12 and portions P2 on both outer sides of two places covered with the sealing cover materials 30, and the sealant 50 is spread throughout the portions covered with the sealing cover materials 30 out of the plurality of the bundled electric wires 12.