A steering system comprising: a steering shaft configured to contract and extend in a column axial direction; a column jacket including an outer jacket having a slit and a pair of clamped portions arranged on opposite sides of the slit and an inner jacket fitted in the outer jacket, the column jacket being configured to contract and extend in the column axial direction; a clamping mechanism including a clamping shaft supported in clamping shaft insertion holes in the clamped portions and an operation lever that rotates the clamping shaft, the clamping mechanism clamping the clamped portions via the clamping shaft to allow the outer jacket to hold the inner jacket; and a tooth locking mechanism that brings first teeth into meshing engagement with second teeth to achieve telescopic locking during clamping by the clamping mechanism, wherein the tooth locking mechanism includes: a first tooth defining member having the first teeth such that the first teeth are arranged in the column axial direction and moving together with the inner jacket; characterized by a support shaft supported in a long groove formed in the outer jacket or a member supported by the outer jacket and extending in the column axial direction such that the support shaft is slidable in the column axial direction; a second tooth defining member that has the second teeth and that is supported by the support shaft so as to be rotatable around a central axis of the support shaft; and an interlocking mechanism including a driving member that rotates together with the clamping shaft and a coupling shaft that couples the second tooth defining member and the driving member together such that the second tooth defining member and the driving member are rotatable and that is parallel to the clamping shaft, the interlocking mechanism interlocking rotation of the clamping shaft with rotation of the second tooth defining member. a steering shaft configured to contract and extend in a column axial direction; a column jacket including an outer jacket having a slit and a pair of clamped portions arranged on opposite sides of the slit and an inner jacket fitted in the outer jacket, the column jacket being configured to contract and extend in the column axial direction; a clamping mechanism including a clamping shaft supported in clamping shaft insertion holes in the clamped portions and an operation lever that rotates the clamping shaft, the clamping mechanism clamping the clamped portions via the clamping shaft to allow the outer jacket to hold the inner jacket; and a tooth locking mechanism that brings first teeth into meshing engagement with second teeth to achieve telescopic locking during clamping by the clamping mechanism, wherein the tooth locking mechanism includes: a first tooth defining member having the first teeth such that the first teeth are arranged in the column axial direction and moving together with the inner jacket; characterized by a support shaft supported in a long groove formed in the outer jacket or a member supported by the outer jacket and extending in the column axial direction such that the support shaft is slidable in the column axial direction; a second tooth defining member that has the second teeth and that is supported by the support shaft so as to be rotatable around a central axis of the support shaft; and an interlocking mechanism including a driving member that rotates together with the clamping shaft and a coupling shaft that couples the second tooth defining member and the driving member together such that the second tooth defining member and the driving member are rotatable and that is parallel to the clamping shaft, the interlocking mechanism interlocking rotation of the clamping shaft with rotation of the second tooth defining member. a first tooth defining member having the first teeth such that the first teeth are arranged in the column axial direction and moving together with the inner jacket; characterized by a support shaft supported in a long groove formed in the outer jacket or a member supported by the outer jacket and extending in the column axial direction such that the support shaft is slidable in the column axial direction; a second tooth defining member that has the second teeth and that is supported by the support shaft so as to be rotatable around a central axis of the support shaft; and an interlocking mechanism including a driving member that rotates together with the clamping shaft and a coupling shaft that couples the second tooth defining member and the driving member together such that the second tooth defining member and the driving member are rotatable and that is parallel to the clamping shaft, the interlocking mechanism interlocking rotation of the clamping shaft with rotation of the second tooth defining member.