A rack and pinion steering gear unit, comprising: a rack shaft that reciprocates according to rotation of a pinion shaft; ball joint sockets (51, 52) that are formed on both end of the rack shaft and have a larger diameter than the rack shaft; a pinion-side housing made of metal that supports a pinion-side end section of the rack shaft where the pinion shaft is located so that sliding movement of the rack shaft is possible, and that can be fastened to the vehicle frame; and a convex engagement section that is formed in the middle section in the axial direction of the rack shaft between the pinion-side end section and the non-pinion-side end section that is on the opposite side from the pinion-side end section, and that has a larger diameter than the rack shaft, characterized in that: as the rack shaft displaces, one of the ball joint sockets that is attached to the pinion-side end section comes in contact with one end of the pinion-side housing, restricting movement of the rack shaft toward the non-pinion side, and the convex engagement section comes in contact with the other end of the pinion-side housing, restricting movement of the rack shaft toward the pinion side; the rack and pinion steering gear unit further comprises: a non-pinion-side housing made of metal that supports the non-pinion-side end section of the rack shaft so that sliding movement of the rack shaft is possible, and that can be fastened to the vehicle frame; and a hollow cylindrical shaped intermediate cylindrical section that is connected to the pinion-side housing on one end, and is connected to the non-pinion-side housing on the other end, and covers the middle section of the rack shaft; and the intermediate cylindrical section is such that all or part of the length has a bellows shape that can expand or contract in the axial direction of the rack shaft. a rack shaft that reciprocates according to rotation of a pinion shaft; ball joint sockets (51, 52) that are formed on both end of the rack shaft and have a larger diameter than the rack shaft; a pinion-side housing made of metal that supports a pinion-side end section of the rack shaft where the pinion shaft is located so that sliding movement of the rack shaft is possible, and that can be fastened to the vehicle frame; and a convex engagement section that is formed in the middle section in the axial direction of the rack shaft between the pinion-side end section and the non-pinion-side end section that is on the opposite side from the pinion-side end section, and that has a larger diameter than the rack shaft, characterized in that: as the rack shaft displaces, one of the ball joint sockets that is attached to the pinion-side end section comes in contact with one end of the pinion-side housing, restricting movement of the rack shaft toward the non-pinion side, and the convex engagement section comes in contact with the other end of the pinion-side housing, restricting movement of the rack shaft toward the pinion side; the rack and pinion steering gear unit further comprises: a non-pinion-side housing made of metal that supports the non-pinion-side end section of the rack shaft so that sliding movement of the rack shaft is possible, and that can be fastened to the vehicle frame; and a hollow cylindrical shaped intermediate cylindrical section that is connected to the pinion-side housing on one end, and is connected to the non-pinion-side housing on the other end, and covers the middle section of the rack shaft; and the intermediate cylindrical section is such that all or part of the length has a bellows shape that can expand or contract in the axial direction of the rack shaft. as the rack shaft displaces, one of the ball joint sockets that is attached to the pinion-side end section comes in contact with one end of the pinion-side housing, restricting movement of the rack shaft toward the non-pinion side, and the convex engagement section comes in contact with the other end of the pinion-side housing, restricting movement of the rack shaft toward the pinion side; the rack and pinion steering gear unit further comprises: a non-pinion-side housing made of metal that supports the non-pinion-side end section of the rack shaft so that sliding movement of the rack shaft is possible, and that can be fastened to the vehicle frame; and a hollow cylindrical shaped intermediate cylindrical section that is connected to the pinion-side housing on one end, and is connected to the non-pinion-side housing on the other end, and covers the middle section of the rack shaft; and the intermediate cylindrical section is such that all or part of the length has a bellows shape that can expand or contract in the axial direction of the rack shaft. a non-pinion-side housing made of metal that supports the non-pinion-side end section of the rack shaft so that sliding movement of the rack shaft is possible, and that can be fastened to the vehicle frame; and a hollow cylindrical shaped intermediate cylindrical section that is connected to the pinion-side housing on one end, and is connected to the non-pinion-side housing on the other end, and covers the middle section of the rack shaft; and the intermediate cylindrical section is such that all or part of the length has a bellows shape that can expand or contract in the axial direction of the rack shaft.