PURPOSE: To provide the title apparatus capable of providing a uniform magnetic field distribution and applying a sufficient magnetic field to a fuel oil, by providing a magnetic field-generating zone having a permanent magnet within a casing equipped with a fuel-feeding port and a discharging port at predetermined positions.

CONSTITUTION: A plurality of axial levers 6 equipped with a plurality of disc- like permanent magnets 4 inserted therein of which the one side 4a serves as a positive pole while the other side 4b serves as a negative pole are arranged in parallel between the two opposite inside walls 1a of a casing 1 having openings of a fuel-feeding port 2 and a discharging port 3 at predetermined positions in such a manner that the opposite faces exhibit the same polarity, thereby forming a magnetic field-generating zone 5.