A grommet formed of rubber or elastomer and externally fittable onto a wire harness extending between a vehicle-body panel and an opening and closing body comprised of a door or a trunk lid of a vehicle, the grommet comprising: a pleated cylindrical section; a curved cylindrical section (3, 4) extending from an end of the pleated cylindrical section; and a cylindrical section (5, 6) arranged at a tip end of the curved cylindrical section (3, 4), wherein: a vehicle-body engagement recess (7, 8) is formed on the outer circumference surface of the cylindrical section (5, 6), or an inner resin member formed with vehicle-body engagement pawls is internally fitted into the cylindrical section (5, 6); and at least one of the outer circumference surface and the inner circumference surface of the curved cylindrical section (3, 4) is provided with reinforcement ribs for resisting buckling; and characterized in that the reinforcement ribs include: opposite end-ring parts (10a, 10b) provided at a boundary between one of the longitudinal ends of the curved cylindrical section (3, 4) and the pleated cylindrical section and at a boundary between the other of the longitudinal ends of the curved cylindrical section (3, 4) and the cylindrical section (5, 6), respectively; a middle-ring part provided at a middle area of the curved cylindrical section (3, 4); and a connection part (10d, 10e) configured to interconnect the opposite end-ring parts (10a, 10b) and the middle-ring part in the axial direction. a pleated cylindrical section; a curved cylindrical section (3, 4) extending from an end of the pleated cylindrical section; and a cylindrical section (5, 6) arranged at a tip end of the curved cylindrical section (3, 4), wherein: a vehicle-body engagement recess (7, 8) is formed on the outer circumference surface of the cylindrical section (5, 6), or an inner resin member formed with vehicle-body engagement pawls is internally fitted into the cylindrical section (5, 6); and at least one of the outer circumference surface and the inner circumference surface of the curved cylindrical section (3, 4) is provided with reinforcement ribs for resisting buckling; and characterized in that the reinforcement ribs include: opposite end-ring parts (10a, 10b) provided at a boundary between one of the longitudinal ends of the curved cylindrical section (3, 4) and the pleated cylindrical section and at a boundary between the other of the longitudinal ends of the curved cylindrical section (3, 4) and the cylindrical section (5, 6), respectively; a middle-ring part provided at a middle area of the curved cylindrical section (3, 4); and a connection part (10d, 10e) configured to interconnect the opposite end-ring parts (10a, 10b) and the middle-ring part in the axial direction. a vehicle-body engagement recess (7, 8) is formed on the outer circumference surface of the cylindrical section (5, 6), or an inner resin member formed with vehicle-body engagement pawls is internally fitted into the cylindrical section (5, 6); and at least one of the outer circumference surface and the inner circumference surface of the curved cylindrical section (3, 4) is provided with reinforcement ribs for resisting buckling; and characterized in that the reinforcement ribs include: opposite end-ring parts (10a, 10b) provided at a boundary between one of the longitudinal ends of the curved cylindrical section (3, 4) and the pleated cylindrical section and at a boundary between the other of the longitudinal ends of the curved cylindrical section (3, 4) and the cylindrical section (5, 6), respectively; a middle-ring part provided at a middle area of the curved cylindrical section (3, 4); and a connection part (10d, 10e) configured to interconnect the opposite end-ring parts (10a, 10b) and the middle-ring part in the axial direction.