A grommet for installing a wire harness into a penetration hole provided on a car body panel of an automobile. The grommet includes a resin inner sleeve that is firmly stored in an enlarged tubular portion of a grommet main body made of an elastomer. The grommet main body includes the enlarged tubular portion at one end of a small diameter tubular portion through which electric wires can be inserted. A fixation locking hook protrudes from a peripheral wall of the inner sleeve and projects past an edge opening of the enlarged tubular portion. A movable locking hook is arranged on another side of the peripheral wall. The movable locking hook includes a movable piece that is located between two side grooves formed in the peripheral wall. A pair of rectifying ribs protrudes past the movable locking hook. Each rectifying rib has an edge portion that is formed at an acute angle and that is inclined towards an inside. The pair of rectifying ribs are insertable into the penetration hole after the fixation locking hook is inserted therein.