A folding device for folding a copy along a line parallel to a direction of forward travel of the copy, the copy being delivered to a folding table having a longitudinal central slit, is disclosed. The folding device includes a crankshaft, disposed below the folding table in line with the central slit, which is rotatably driven about a central axis of rotation parallel to the direction of forward travel of the copy. The folding device also includes a folding cylinder having a radius R and an external surface S, which is rotatably mounted about a central geometric axis on the crankshaft. The central geometric axis is parallel to the central axis of rotation of the crankshaft and offset with respect to the central axis of rotation by a distance equal to the radius R. Each time a copy is folded, the crankshaft makes a complete revolution about the central axis of rotation simultaneously driving the folding cylinder through its own rotational movement about the central geometric axis, so that any point on the external surface S of the folding cylinder moves along a straight line of length equal to four times the radius R.