The invention proposes a device for adjusting the length of a wristband or bracelet including a base plate and an adjusting link, the adjusting link being hinged on the base plate via at least one connecting rod which is hinged on the base plate via a main pin which is hinged on the adjusting link via a secondary pin, wherein the adjusting link is arranged so as to slide relative to the base plate, including a locking device allowing the adjusting link to catch on an anchoring element arranged on the base plate in at least two indexed longitudinal positions, respectively defining two lengths of the bracelet, characterized in that the anchoring element is arranged on the main pin. The invention also proposes a bracelet fitted with this adjustment device and a watch fitted with such a bracelet.