The invention concerns an equipment and a method in a twin-wire former, in which a partly pre-drained or non-drained fibre stock is passed to between the forming wires of the web former in the vicinity of the former roll (11) or of a water drain box, in which connection water is drained out of the stock web by means of the former roll (11) or the water drain box. The twin-wire former comprises a rib (20) in connection with the former roll (11) or the water drain box in the lateral area of the wires (H2), which rib has been fitted to control the running of the second forming wire (H2) passed from the gap roll. By means of the rib (20), in the lateral area of the wire runs, the point at which said forming wire (H2) reaches contact with the first forming wire in connection with the former roll (11) or the water drain box is shifted further away in the machine direction. The rib (20) is an oblong structure, which has a maximal height (Hmax) in the middle area of the rib (20).