Adjustable connecting device comprised by an alignment body provided with at least one vertical adjustment channel in one of its surfaces which is capable of receiving the sliding piece for vertical adjustment; said alignment body having at least one vertical adjustment aperture in its surface, which aperture coincides with the position of the toothed rack of the sliding piece for vertical adjustment and is capable of receiving the vertical toothed adjustment pinion whose toothing corresponds to the toothing of the toothed rack; said sliding piece for vertical adjustment being provided with the corresponding slot-shaped aperture in the transverse direction and the corresponding toothed rack; wherein the adjustment device is completed by the fastening screw for fastening the decorative drawer front which secures the decorative drawer front.