PURPOSE: To disperse and pulverize the fuel oil component, separate the intractable substance by centrifugal force, and improve the combustibility of the fuel oil, by introducing the fuel oil in a casing having magnetic field, and causing cavitation and at the same time, rotating at a high speed.

CONSTITUTION: The rotor 3 having a rough surface placed closely opposite to the stator is rotated at a high speed in the casing 2 having a magnetic field generated by the coil 17. The fuel oil is introduced into the casing through the line 8, and is forced to generate cavitation in the oil. At the same time, the oil is rotated at a high speed to disperse, pulverize and activate the components such as sludge, asphaltene, etc. of the fuel oil, and to centrifuge the intractable component at a part of the rotor to obtain refined fuel oil.