Positioning projections for engaging recesses in an outer peripheral surface of a mating member project from an inner peripheral surface of a grommet, and the position of a minimum inside diameter portion of each positioning projection after being fitted to the mating member is offset from interference of a jointing member. In a case where the positioning projections are formed in front of a sealing projection, a larger cylindrical portion is absent around their outer peripheries. Therefore, the enlargement of the diameter of the grommet during fitting to the mating member is not restricted, resistance during fitting is alleviated, and the positioning projections are engaged in the recesses with large elastic reaction force. Hence, a click feel is excellent.