A method and a device for controlling the flow of the molten metal in non-solidified portions of a cast strand in connection with casting of metal. A mould (11) is supplied with at least one primary flow (20) of molten metal and at least one strand (1) is formed in the mould. At least one static or periodic low-frequency magnetic field (10) is applied to act with a maximum magnetic field strength in the mould exceeding 1000 Gauss in the path of the inflowing molten metal to brake and divide the primary flow (20) of molten metal flowing into the mould and to control any secondary flows (21, 22) arising. The static magnetic field (10) acts over essentially the whole width (W) of the cast strand (1) formed in the mould, whereby the magnetic field strength in a plane across the casting direction, on a level with the centre of the range of action of the magnetic field (10), varies within an interval of 60 to 100 per cent of its maximum value, while at the same time the field strength on a level with the upper surface/the meniscus of the molten metal amounts to at most 500 Gauss. (FIG. 1 )