A grommet comprising: a fitting body causing a circumferential edge portion of a through hole having a circular shape and provided in a wall body (Pw) to be fitted into a fitting groove having an annular shape and provided in an outer wall, and causing a harness body (We) routed along a hole axis of the through hole in a space in the outer wall to be extracted from the space through a first draw-out aperture having a circular shape and disposed at a first axial end and a second draw-out aperture having a circular shape and disposed at a second axial end; a first cylinder having a cylinder axis coaxial with an axis of the fitting body, projecting outward from a circumferential edge portion of the first draw-out aperture, and causing the harness body (We) in the space to be extracted through inside of the first cylinder; and a second cylinder having a cylinder axis coaxial with the axis of the fitting body, projecting outward from a circumferential edge portion of the second draw-out aperture, and causing the harness body (We) in the space to be extracted through inside of the second cylinder, wherein the fitting body includes a cylindrical portion having an outer circumferential wall surface joined to the fitting groove at a position closer to the first cylinder than the fitting groove in the outer wall, and gradually reduced in diameter as being away coaxially from the fitting groove, a plurality of ribs rising from the outer circumferential wall surface of the cylindrical portion and disposed on the outer circumferential wall surface at equal intervals in a circumferential direction, and each extending on the outer circumferential wall surface at least from a position equal in diameter to the circumferential edge portion of the through hole to a radially outer end, a first support portion provided for each of the ribs and supporting a side, adjacent to the outer circumferential wall surface, of a first side wall of the rib on a first side in the circumferential direction, and a second support portion provided for each of the ribs and supporting a side, adjacent to the outer circumferential wall surface, of a second side wall of the rib on a second side in the circumferential direction, the rib is shaped to enable elastic deformation in the circumferential direction, and the first support portion and the second support portion project from the outer circumferential wall surface to be high enough to suppress elastic deformation of the rib in the circumferential direction toward the outer circumferential wall surface. a fitting body causing a circumferential edge portion of a through hole having a circular shape and provided in a wall body (Pw) to be fitted into a fitting groove having an annular shape and provided in an outer wall, and causing a harness body (We) routed along a hole axis of the through hole in a space in the outer wall to be extracted from the space through a first draw-out aperture having a circular shape and disposed at a first axial end and a second draw-out aperture having a circular shape and disposed at a second axial end; a first cylinder having a cylinder axis coaxial with an axis of the fitting body, projecting outward from a circumferential edge portion of the first draw-out aperture, and causing the harness body (We) in the space to be extracted through inside of the first cylinder; and a second cylinder having a cylinder axis coaxial with the axis of the fitting body, projecting outward from a circumferential edge portion of the second draw-out aperture, and causing the harness body (We) in the space to be extracted through inside of the second cylinder, wherein the fitting body includes a cylindrical portion having an outer circumferential wall surface joined to the fitting groove at a position closer to the first cylinder than the fitting groove in the outer wall, and gradually reduced in diameter as being away coaxially from the fitting groove, a plurality of ribs rising from the outer circumferential wall surface of the cylindrical portion and disposed on the outer circumferential wall surface at equal intervals in a circumferential direction, and each extending on the outer circumferential wall surface at least from a position equal in diameter to the circumferential edge portion of the through hole to a radially outer end, a first support portion provided for each of the ribs and supporting a side, adjacent to the outer circumferential wall surface, of a first side wall of the rib on a first side in the circumferential direction, and a second support portion provided for each of the ribs and supporting a side, adjacent to the outer circumferential wall surface, of a second side wall of the rib on a second side in the circumferential direction, the rib is shaped to enable elastic deformation in the circumferential direction, and the first support portion and the second support portion project from the outer circumferential wall surface to be high enough to suppress elastic deformation of the rib in the circumferential direction toward the outer circumferential wall surface.