In order to form two longitudinal folds in a material web, there are two plow folding units which extend in the vertical direction and are arranged behind one another in the movement direction of the material web. Each of the plow folding units has two guide elements for the material web, which guide elements are arranged in the manner of a gable or saddle roof. The guide elements are arranged behind one another in the movement direction of the material web and enclose a folding angle between them. The folding angle between the guide elements of the second plow folding unit which is arranged downstream of the first plow folding unit has a magnitude of at least 100°, preferably of at least 140°.