A rack-and-pinion steering system comprising: a pinion shaft having pinion teeth; a rack shaft formed with rack teeth formed in a first area of an outer circumferential surface of the rack shaft and which mesh with the pinion teeth; and a rack bush supporting the rack shaft so that the rack shaft slides in an axial direction of the rack shaft, the rack bush comprising: a teeth side support portion in contact with a second area of the outer circumferential surface to support the rack shaft from a teeth side where the rack teeth are formed, the second area lying adjacent to the first area in the axial direction, and a back side support portion in contact with a third area of the outer circumferential surface to support the rack shaft from a back side which is a side other than the teeth side, the third area lying in a position out of the first area in a circumferential direction around an axis of the rack shaft, wherein the rack bush has an inner circumferential surface that fits on the outer circumferential surface of the rack shaft, and characterized in that the rack bush includes relief portions which are provided on the inner circumferential surface in positions which coincide with both end portions of the first area in the circumferential direction and which sink so as to be separated away from the end portions. a pinion shaft having pinion teeth; a rack shaft formed with rack teeth formed in a first area of an outer circumferential surface of the rack shaft and which mesh with the pinion teeth; and a rack bush supporting the rack shaft so that the rack shaft slides in an axial direction of the rack shaft, the rack bush comprising: a teeth side support portion in contact with a second area of the outer circumferential surface to support the rack shaft from a teeth side where the rack teeth are formed, the second area lying adjacent to the first area in the axial direction, and a back side support portion in contact with a third area of the outer circumferential surface to support the rack shaft from a back side which is a side other than the teeth side, the third area lying in a position out of the first area in a circumferential direction around an axis of the rack shaft, wherein the rack bush has an inner circumferential surface that fits on the outer circumferential surface of the rack shaft, and characterized in that the rack bush includes relief portions which are provided on the inner circumferential surface in positions which coincide with both end portions of the first area in the circumferential direction and which sink so as to be separated away from the end portions. a teeth side support portion in contact with a second area of the outer circumferential surface to support the rack shaft from a teeth side where the rack teeth are formed, the second area lying adjacent to the first area in the axial direction, and a back side support portion in contact with a third area of the outer circumferential surface to support the rack shaft from a back side which is a side other than the teeth side, the third area lying in a position out of the first area in a circumferential direction around an axis of the rack shaft, wherein the rack bush has an inner circumferential surface that fits on the outer circumferential surface of the rack shaft, and characterized in that the rack bush includes relief portions which are provided on the inner circumferential surface in positions which coincide with both end portions of the first area in the circumferential direction and which sink so as to be separated away from the end portions.