To make folds of a bellows part of an elongated grommet unlikely to be conspicuous.

A grommet which protects a wire harness cabled between a vehicle body and a door connected to the vehicle body by inserting the wire harness internally comprises: a bellows cylinder section including a bellows part in which crest portions and valley portions are alternately provided in a length direction and which can be elongated/contracted; and a pair of mounting parts which are provided in both end portions of the bellows cylinder section and mounted to a vehicle body side and a door side, respectively. In the bellows part, the neighboring crest portion and valley portion are thinner than a slope portion connecting the crest portion and the valley portion.