Applicator of jointing tape for joining two sheets of plasterboard, the applicator comprising a payout device for paying out a jointing tape that comes in a roll and a mud chamber through which the tape is paid out, in use, the chamber having, with reference to the position of use, a tape inlet slot formed between a free end of a rear wall of the chamber and a first free end of a lower wall of the chamber, and a tape outlet slot formed between a free end of a frontal wall of the chamber and a second free end of the lower wall of the chamber, the chamber further comprising two lateral walls, one of which constitutes a removable side cover providing access to the inside of the chamber, the outlet slot having a determined height and being equipped with heightwise adjustment means, the adjusting means comprising: - a plate for adjusting the height of said outlet slot, said plate being arranged inside the chamber against an interior face of the frontal wall of the chamber, characterized in that the adjusting means further comprise: - a mounting plate fixed with the ability to slide against an exterior contact face of the frontal wall of the chamber, the contact face comprising a sliding guide, equipped with an oblong orifice, the mounting plate comprising a sliding end stop collaborating in sliding with the sliding guide and equipped with a central hole; - a coupling and clamping spindle for coupling and clamping the plate, said spindle being engaged in an orifice of the plate, in the oblong hole of the sliding guide, and in the central hole of the sliding end stop - means for tensioning/slackening-off the coupling and clamping spindle to allow the mounting plate and the plate to be clamped against/loosened off from the frontal wall of the chamber. - a plate for adjusting the height of said outlet slot, said plate being arranged inside the chamber against an interior face of the frontal wall of the chamber, characterized in that the adjusting means further comprise: - a mounting plate fixed with the ability to slide against an exterior contact face of the frontal wall of the chamber, the contact face comprising a sliding guide, equipped with an oblong orifice, the mounting plate comprising a sliding end stop collaborating in sliding with the sliding guide and equipped with a central hole; - a coupling and clamping spindle for coupling and clamping the plate, said spindle being engaged in an orifice of the plate, in the oblong hole of the sliding guide, and in the central hole of the sliding end stop - means for tensioning/slackening-off the coupling and clamping spindle to allow the mounting plate and the plate to be clamped against/loosened off from the frontal wall of the chamber. - a mounting plate fixed with the ability to slide against an exterior contact face of the frontal wall of the chamber, the contact face comprising a sliding guide, equipped with an oblong orifice, the mounting plate comprising a sliding end stop collaborating in sliding with the sliding guide and equipped with a central hole; - a coupling and clamping spindle for coupling and clamping the plate, said spindle being engaged in an orifice of the plate, in the oblong hole of the sliding guide, and in the central hole of the sliding end stop - means for tensioning/slackening-off the coupling and clamping spindle to allow the mounting plate and the plate to be clamped against/loosened off from the frontal wall of the chamber.