A steering system comprising: a steering shaft that is configured to contract and extend in a column axial direction during telescopic adjustment; 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 during telescopic adjustment; a clamping mechanism including a clamping shaft supported in clamping shaft through-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 so that the outer jacket holds the inner jacket at a predetermined position within a telescopic stroke range; 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, characterised by the fact that: 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; a second tooth defining member including a first portion rotatably supported around a support and a second portion located away from the first portion and having the second teeth; and an interlocking mechanism that interlocks motion of the second tooth defining member with rotation of the clamping shaft a first guide mechanism that guides the first portion in the column axial direction, and a second guide mechanism that guides the second portion in an orthogonal direction orthogonal to the column axial direction while the first teeth and the second teeth are in a meshing engagement state. a steering shaft that is configured to contract and extend in a column axial direction during telescopic adjustment; 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 during telescopic adjustment; a clamping mechanism including a clamping shaft supported in clamping shaft through-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 so that the outer jacket holds the inner jacket at a predetermined position within a telescopic stroke range; 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, characterised by the fact that: 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; a second tooth defining member including a first portion rotatably supported around a support and a second portion located away from the first portion and having the second teeth; and an interlocking mechanism that interlocks motion of the second tooth defining member with rotation of the clamping shaft a first guide mechanism that guides the first portion in the column axial direction, and a second guide mechanism that guides the second portion in an orthogonal direction orthogonal to the column axial direction while the first teeth and the second teeth are in a meshing engagement state. 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; a second tooth defining member including a first portion rotatably supported around a support and a second portion located away from the first portion and having the second teeth; and 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; a second tooth defining member including a first portion rotatably supported around a support and a second portion located away from the first portion and having the second teeth; and an interlocking mechanism that interlocks motion of the second tooth defining member with rotation of the clamping shaft a first guide mechanism that guides the first portion in the column axial direction, and a second guide mechanism that guides the second portion in an orthogonal direction orthogonal to the column axial direction while the first teeth and the second teeth are in a meshing engagement state.