Abstract: A ski boot comprising: a rigid shell which is shaped so as to accommodate the foot of the user, and has a lower part structured to be able to couple to a ski binding device; a rigid cuff which is shaped so as to enclose the lower part of the leg of the user, and is pivotally joined to the shell so as to be able to swing about a rotation axis substantially perpendicular to the midplane of the boot; and a cuff locking device which is located on the cuff and is selectively adapted to rigidly connect the cuff to the shell to prevent the cuff from swinging on the shell; the cuff locking device, in turn, comprising a movable arm which is pivotally joined to the cuff so as to be able to rotate to and from a locking position in which the movable arm extends downwards and arranges its distal end in abutment on an anchorage structure present on said shell, and an elastic assembly which is adapted to bring and elastically retain the movable arm in the locking position, and which basically consists of a telescopic stem t