A steering system includes an inner column; an outer column including a guide tube part that supports the inner column to be movable in an axial direction and a holding tube part in which a slit extending in the axial direction is formed; and a telescopic adjustment mechanism that switches between a locked state in which an interval of the slit is reduced and movement of the inner column is regulated and an unlocked state in which the interval of the slit is increased and the movement of the inner column is allowed. An inner circumferential surface of the guide tube part has support surfaces that slidably support an outer circumferential surface of the inner column, and flanks located on the same circumference as the support surfaces and are separated from the outer circumferential surface of the inner column in a radial direction.