To reduce an insertion force required when a grommet with a resin inner is installed in a panel through hole, and reliably prevent half fitting with a single motion.

The resin inner 20 is configured by rotatably coupling together split resin inners 20A, 20B split in the axial line direction at the center line of a short axis around a rotating shaft 28. When the grommet 10-1 is installed in a panel through hole H, the following procedure is used: the split resin inners 20A, 20B are rotated around the rotating shaft 28 to open the base ends of halved cylindrical portions 21A, 21B and the tips are narrowed and inclined for insertion into the through hole H; thereafter, the base ends of the halved cylindrical portions 21A, 21B are closed and the locking portion 31 provided on halved flange portions 22A, 22B and a locked frame portion 32 are locked together; and first to third anchoring lugs 23A, 23B, 24A, 24B, 25A, 25B, protruded from the outer circumferential surfaces on the tip side of the halved cylindrical portions 21A, 21B are anchored to the rim of the through hole H.