PURPOSE: To uniformly process liquid fuel in a magnetic field by providing a magnet in a vessel in which the fuel is passed.

CONSTITUTION: A magnet 50 is provided in a vessel body 30. Liquid fuel fed from an inlet 10 into the body 30 is passed through a magnetic field formed by the magnet 50, and fed out of an outlet 20 (in a direction of an arrow). Here, when the body 30 is formed of a magnetic material such as general-purpose structural steel, etc., the magnetic field can be shut-off to an exterior, dusts containing magnetic sand, iron content are not adhered to an outer surface of the body 30 for convenience. Thus, intensity of the field is not reduced due to a material of the tube, but the fuel can be sufficiently and uniformly magnetic field-processed.