A cutting device for an automatic sewing machine, including a knife (2) and a knife guard (3) which projects the fingers of the operator. The knife (2) is capable of being lowered to a cutting area in a cutting plane (S) only when the knife guard (3) is in its protecting position. The knife (2) and knife guard (3) are driven simultaneosuly by a single drive, the knife guard (3) reaching the cutting plane (S) earlier than the knife (2). If the knife guard (3) cannot substantially reach its protective position, then the downward movement of the knife (2) is mechanically blocked, preventing further movement of the knife (2). This mechanical blocking is carried out by the coaction of a lever (20) which is connected to the knife guard (3) by a connecting member (21), the lever (20) being moveable in translation and rotation, and by a lever (19), which is moveable rotationally only and has a stop (37) thereon for blocking movement of the knife (2) when the knife guard (3) is not in its protective position. The stop (37) is responsive both to the drive (5) and to the degree to which the knife guard (3) has been lowered.