A cylindrical rack bushing is interposed between a tubular housing and a rack shaft inserted coaxially through the housing, and supports the rack shaft so that the rack shaft is slidable in an axial direction. The rack bushing has an inner periphery on which an inward protruding portion protruding toward an inner side of the rack bushing in a radial direction is formed. The inward protruding portion includes a top portion that is in sliding contact with the rack shaft in a line contact manner or a point contact manner.