PURPOSE: To improve the workability eliminating need of insertion work of a wire harness into a grommet and provide reliable water-proofness by filling the void between electric wires of a wire harness to be insertion-molded with a sealing agent.

CONSTITUTION: A grommet is one to which a wire harness is attached by inserting the wire harness into a through hole of a diaphragm in water-proofing condition and grommet 1 has a stopping groove 1d for the periphery of the through hole in the outer circumferential face and also has an electric wire insertion hole 1c aloong the axial line. The grommet is composed by molding thermally plastic resin in molding dies while a wire harness 2 coated with a thermally curable sealing agent 3 being molded and thus the wire harness 2 in which the void among the electric wires is filled with the sealing agent 3 hardened at the time of molding is inserted into the electric wire insertion hole.