To incorporate a wiring harness by an insertion operation in one direction into a box, without drawing back the wiring harness towards an engine room side.

A wiring harness is inserted into a box, which is provided in the engine room of a car and has a built-in electronic controller through a grommet attached to a through-hole formed in a sidewall of the box. The through-hole 12 forms a barring 13. The grommet 15 has a small diameter cylindrical part through which the wiring harness is inserted, an expanded diameter cylindrical part 15b and retaining nails 15c made to be protruded from the tip part of an expanded diameter cylindrical part 15b. An inner member 20 is attached from the inside of the box, and the part of the expanded diameter cylindrical part 15b positioned on the inner circumference of the barring 13 is pressed by the inner member 20 to press the sealing protrusion of the grommet against the barring 13.