A locking claw (23a) to be locked to a through-hole (H) projects outwardly from a peripheral wall (21) of a resinous inner member (20). At least one pair of locking holes (24) is formed on a locking flange part (22) projecting from the peripheral wall (21). An annular concavity (12a) (13a), on which the locking flange part (22) fits, is formed on an inner peripheral surface of a large-diameter cylindrical part (12, 13). Locking projections (12a-1, 13a-1) project from a leading end of a side wall of the annular concavity (12a, 13a). The locking projections (12a-1, 13a-1) are inserted into and locked with the locking holes (24). Locking claws (123a-126a) project from the resinous inner member (120) and are locked to a through-hole (H1) of the body panel (P1). A pair of flexible locking pieces (123-126), to be locked to the body panel (P1), project from each of a shorter side and a longer side of an elliptic peripheral wall (121) of the resinous inner member (120) projecting from an open end of the large-diameter cylindrical part (112, 113). A leading end of the locking pieces (123-126) project outwardly from an intermediate position of an outer surface of the locking pieces (123-126). The locking pieces on the longer side are curved longitudinally to form a circular arc shape.