A folding device, intended to fold a continuous web of flexible material on itself which is made to pass therethrough, usable in machines for manufacturing packaging from a continuous web of material, said device comprising in a forward direction of the web a main folder and an auxiliary folder, aligned, both inscribed in planes perpendicular to a reference plane and positioned forming an angle (α) with each other, - the main folder having an essentially triangular shape the sides of which, converging towards the reference plane without meeting each other, determine a set of first folding edges intended to gradually bend the web to face two longitudinal portions of the same connected by a bottom portion; - the auxiliary folder having a triangular shape the sides of which, converging in the reference plane, determine a set of second folding edges intended to gradually bend the bottom portion towards the inside of the web; - the first folding edges being movably mounted on the body of the main folder, such that the coordinated movement thereof towards or in the opposite direction to the reference plane, and therefore the move towards or away each other of the converging ends of the first folding edges, enables the opening or closing of the triangle shape to be regulated and thus the width of the bottom portion of the web; wherein - the folding device comprises positioning means for positioning the main and auxiliary folders such that each of the ends of the first folding edges of the main folder adjust over a respective second folding edge of the auxiliary folder; the folding device being characterized in that - the auxiliary folder is linked to the main folder able to move along an adjustment axis parallel to the bisector of the angle (α) formed between the main and auxiliary folders (2, 3). - the main folder having an essentially triangular shape the sides of which, converging towards the reference plane without meeting each other, determine a set of first folding edges intended to gradually bend the web to face two longitudinal portions of the same connected by a bottom portion; - the auxiliary folder having a triangular shape the sides of which, converging in the reference plane, determine a set of second folding edges intended to gradually bend the bottom portion towards the inside of the web; - the first folding edges being movably mounted on the body of the main folder, such that the coordinated movement thereof towards or in the opposite direction to the reference plane, and therefore the move towards or away each other of the converging ends of the first folding edges, enables the opening or closing of the triangle shape to be regulated and thus the width of the bottom portion of the web; wherein - the folding device comprises positioning means for positioning the main and auxiliary folders such that each of the ends of the first folding edges of the main folder adjust over a respective second folding edge of the auxiliary folder; the folding device being characterized in that - the auxiliary folder is linked to the main folder able to move along an adjustment axis parallel to the bisector of the angle (α) formed between the main and auxiliary folders (2, 3).