Abstract: Device for the pressing of sheets during folding, including a first roller (2a) and a second roller (2b) which are positioned opposite each other and have rotation axes (3a, 3b) which are parallel to each other, and first permanent magnets (13a) engaged to the first roller (2a) and second permanent magnets (13b) engaged to the second roller (2b), the first permanent magnets (13a) and the second permanent magnets (13b) having opposite polarities facing each other. The process consists in applying mutual approach forces to the rollers which decrease as the distance between the same rollers increases.