The objective of the present invention is to reduce the impact of production variability in a radius of curvature of a rear surface of a rack bar, for example, while enlarging a region of contact withthe rack bar. A concave surface (330) is used as a rack guide seat (32) sliding surface (33). In a YZ cross section perpendicular to an axial direction of a rack bar, the concave surface (330) includes: a pair of first arcuate surfaces (331A, 331B) which are disposed on a peripheral edge side (320) of the sliding surface (33), from two positions of contact TA, TB with a rack bar rear surface (22), the positions of contact TA, TB having line symmetry with respect to a straight line O3 joining a center O of a rack bar (20) with a bottom portion center C of the sliding surface (33), and which have line symmetry with respect to the straight line O3; and a pair of second arcuate surfaces (332A, 332B) which are disposed on a bottom portion side (321) of the sliding surface (33), from the positions of contact TA, TB, and which have line symmetry with respect to the straight line O3. With regard to gaps to the rack bar rear surface (22) in positions separated by the same distance from the positions of contact TA, TB, the gaps from the first arcuate surfaces (331A, 331B) are greater than the gaps from the second arcuate surfaces (332A, 332b).