The object of the invention is an apparatus (50) for magnetic treatment of fluids, comprising a substantially cylindrical housing (6), having a bottom wall (61), a top wall (62), and a sidewall (60) running around the circumference of the bottom wall (61) and of the top wall (62) of the housing; at least one inlet opening (2, 3) and at least one outlet opening (4) formed in a wall of the housing (6); at least one magnet (8) connected to the housing (6), wherein the magnetic field of the magnet intrudes into the housing; wherein one or more inlet tubes (30) are connected to the one or more inlet openings (2, 3), wherein the inlet tubes are at least partially tangential at least in the proximity of the inlet opening. As a result of this configuration, the velocity vector of the fluid to be treated has a significant tangential component during most of its travel through the apparatus and thus the fluid crosses the magnetic field lines of the magnets having their magnetic axes oriented parallel with the centerline of the housing such that the angle formed between said field lines and said velocity vector is large.