Abstract: A cutting device for a roll of protective film includes an elongated positioning unit which has two side walls, a top wall interconnecting the top ends of the side walls so as to define a sliding space among the side and top walls, and a longitudinally extending slot formed through the top wall and communicated with the sliding space. A cutter includes a sliding body placed on the positioning unit and having a rear portion and a front portion which has a rearwardly and downwardly inclined front end surface and a notch formed in the bottom surface thereof. A blade is mounted in the notch and extends rearwardly and downwardly from the sliding body in such a manner that the cutting edge of the blade is aligned with the front end surface of the sliding body. A guide unit includes two vertical plates projecting downwardly from the rear portion of the sliding body through the slot of the positioning unit, and two horizontal plates that project outwardly from lower ends of the vertical plates.