A steering system comprising: a housing having a hollow shape; a steering operation shaft housed in the housing, the steering operation shaft having a first external thread groove, the steering operation shaft having a second external thread groove, and the steering operation shaft configured to move in an axial direction of the steering operation shaft to steer right and left steered wheels (6R, 6L); a first nut screwed with the first external thread groove and rotatably supported inside the housing; a second nut screwed with the second external thread groove and rotatably supported inside the housing; a first drive source that generates a first drive force; a second drive source that operates independently of the first drive source to generate a second drive force; a first power transfer unit that transfers the first drive force to the first nut and rotates the first nut to apply an axial force to the steering operation shaft; a second power transfer unit that transfers the second drive force to the second nut and rotates the second nut to apply an axial force to the steering operation shaft; a position detection sensor that is provided in the housing and that detects an axial position of the steering operation shaft; and a control device that controls the first drive source and the second drive source using a detection result of the position detection sensor, characterized in that the first external thread groove is one of a left-hand thread groove and a right-hand thread groove, and the second external thread groove is the other one of the left-hand thread groove and the right-hand thread groove, in that the outer periphery of the steering operation shaft has a mark (81, 82, 83) at positions where the first and second rolling grooves (201, 202) are not provided, and in that the position detection sensor detects an axial position of the steering operation shaft by using the mark (81, 82, 83), wherein the position detection sensor is fixed at a position at which the position detection sensor faces the mark (81, 82, 83). a housing having a hollow shape; a steering operation shaft housed in the housing, the steering operation shaft having a first external thread groove, the steering operation shaft having a second external thread groove, and the steering operation shaft configured to move in an axial direction of the steering operation shaft to steer right and left steered wheels (6R, 6L); a first nut screwed with the first external thread groove and rotatably supported inside the housing; a second nut screwed with the second external thread groove and rotatably supported inside the housing; a first drive source that generates a first drive force; a second drive source that operates independently of the first drive source to generate a second drive force; a first power transfer unit that transfers the first drive force to the first nut and rotates the first nut to apply an axial force to the steering operation shaft; a second power transfer unit that transfers the second drive force to the second nut and rotates the second nut to apply an axial force to the steering operation shaft; a position detection sensor that is provided in the housing and that detects an axial position of the steering operation shaft; and a control device that controls the first drive source and the second drive source using a detection result of the position detection sensor, characterized in that the first external thread groove is one of a left-hand thread groove and a right-hand thread groove, and the second external thread groove is the other one of the left-hand thread groove and the right-hand thread groove, in that the outer periphery of the steering operation shaft has a mark (81, 82, 83) at positions where the first and second rolling grooves (201, 202) are not provided, and in that the position detection sensor detects an axial position of the steering operation shaft by using the mark (81, 82, 83), wherein the position detection sensor is fixed at a position at which the position detection sensor faces the mark (81, 82, 83).