Two flat surface portions are provided on portions of a rack shaft away from rack teeth and a back surface in the circumferential direction. The two flat surface portions are parallel to each other. A rotation stopping member has a case and a low-friction member. The hollow portion provided inside the case includes two flat surface portions that face each other in a direction Y and extend in parallel with each other, and two flat surface portions that face each other in a direction Z and extend orthogonally to the flat surface portions. A slight clearance is provided between the outer surface of the rack shaft and the inner surface of the rotation stopping member (low-friction member). The rotation stopping member is disposed on the outer periphery of the rack shaft. The outer periphery of the rotation stopping member is fixed to the inner periphery of a rack housing.