A motor vehicle steering system comprising: a tubular housing fixed to a center portion of an axle beam (26; 26A) having the center portion fixed to a vehicle body; a steered shaft that has first and second end portions (181, 182) projecting from the housing and is driven in an axial direction according to an operation of a steering member; a first knuckle that is supported swingably around a first king pin fixed to the first end portion of the axle beam (26; 26A) and supports a first rear wheel as a steered wheel rotatably; a second knuckle that is supported swingably around a second king pin fixed to the second end portion of the axle beam (26; 26A) and supports a second rear wheel as a steered wheel rotatably; a first tie rod that joins the first end portion of the steered shaft to the first knuckle; a second tie rod that joins the second end portion of the steered shaft to the second knuckle; a first counter load application mechanism that applies a counter load against a radial load in the front-rear direction transmitted to the first end portion of the steered shaft via the first rear wheel, the first knuckle, and the first tie rod as a turning reaction force from a road surface to the first end portion of the steered shaft; and a second counter load application mechanism that applies a counter load against a radial load in the front-rear direction transmitted to the second end portion of the steered shaft via the second rear wheel, the second knuckle, and the second tie rod as a turning reaction force from the road surface, characterized in that each of the first counter load application mechanism and the second counter load application mechanism includes a motion conversion mechanism that converts torsional motion of a corresponding end portion (261, 262) of the axle beam (26; 26A) caused by a ground contact reaction force (Q1, Q2) of a corresponding rear wheel (6L, 6R) via a corresponding knuckle (25L, 25R) and a corresponding king pin (27L, 27R) into motion in the front-rear direction of a corresponding end portion (181, 182) of the steered shaft. a tubular housing fixed to a center portion of an axle beam (26; 26A) having the center portion fixed to a vehicle body; a steered shaft that has first and second end portions (181, 182) projecting from the housing and is driven in an axial direction according to an operation of a steering member; a first knuckle that is supported swingably around a first king pin fixed to the first end portion of the axle beam (26; 26A) and supports a first rear wheel as a steered wheel rotatably; a second knuckle that is supported swingably around a second king pin fixed to the second end portion of the axle beam (26; 26A) and supports a second rear wheel as a steered wheel rotatably; a first tie rod that joins the first end portion of the steered shaft to the first knuckle; a second tie rod that joins the second end portion of the steered shaft to the second knuckle; a first counter load application mechanism that applies a counter load against a radial load in the front-rear direction transmitted to the first end portion of the steered shaft via the first rear wheel, the first knuckle, and the first tie rod as a turning reaction force from a road surface to the first end portion of the steered shaft; and a second counter load application mechanism that applies a counter load against a radial load in the front-rear direction transmitted to the second end portion of the steered shaft via the second rear wheel, the second knuckle, and the second tie rod as a turning reaction force from the road surface, characterized in that each of the first counter load application mechanism and the second counter load application mechanism includes a motion conversion mechanism that converts torsional motion of a corresponding end portion (261, 262) of the axle beam (26; 26A) caused by a ground contact reaction force (Q1, Q2) of a corresponding rear wheel (6L, 6R) via a corresponding knuckle (25L, 25R) and a corresponding king pin (27L, 27R) into motion in the front-rear direction of a corresponding end portion (181, 182) of the steered shaft.