A device for braking a flow of molten metal (5) in a device for continuous or semi-continuous casting of metals in a mould (2) which is provided with opposite broad sides (4) and opposite short sides (3), said device comprising at least one magnet core (1), said at least one core facing one of the short sides (3) of the mould (2) for the purpose of generating a magnetic field (B) and an induced current (i) in a region of the molten metal (5) adjacent the short side (3). The core (1) is arranged in such a way that the magnet field (B) which is generated in said region generally has a direction perpendicular from the short side (3) of the mould (2) towards the centre of the latter.