NOVELTY - The device comprises a pipe (2) for guiding fluids and three pairs of magnets (3) arranged one behind the other. Magnetic fields penetrate into an interior of the pipe. The magnets are made of cylindrical construction, and are arranged outside of the pipe. The pairs of magnets of are aligned with one another on opposing sides of a pipe wall, and have end faces (4) directed towards the pipe. Each magnet has a line pattern of alternating magnet polarity. The line pattern is aligned perpendicular to a flow direction of the fluid. The magnets are arranged in a housing (5).    USE - The device is useful for magnetic treatment of a hydrocarbon-containing fluid (claimed), where the fluid includes diesel, petrol, kerosene, fuel oil, heavy oil and vegetable oils.    ADVANTAGE - The exchangeable device has simple structure and lightweight, is easy to maintain and use, and efficiently treats the hydrocarbon-containing fluid with reduced emission of carbon dioxide.    DETAILED DESCRIPTION - The device comprises a pipe (2) for guiding fluids and three pairs of magnets (3) arranged one behind the other. Magnetic fields penetrate into an interior of the pipe. The magnets are made of cylindrical construction, and are arranged outside of the pipe. The pairs of magnets of are aligned with one another on opposing sides of a pipe wall, and have end faces (4) directed towards the pipe. Each magnet has a line pattern of alternating magnet polarity. The line pattern is aligned perpendicular to a flow direction of the fluid. The magnets are arranged in a housing (5), have tubular shape, and are fixed with plastic parts. Axes of two series-opposed magnet pairs have an angle in the flow direction. The magnets are further arranged in a drum, which is axially rotated on a conduit. The drum is connected with an electric drive. The rotation of the drum is controlled by a controller that is connected with a sensor for measuring activation of the fluid.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a magnet.    Pipe (2)    Magnets (3)    End faces of magnets (4)    Housing (5)    End caps. (7)