Abstract: A device for processing liquid fuel capable of substantially reducing noxious materials comprised in exhaust gas emitted from heat engine. Device (10) for processing liquid fuel according to this invention is a device (10) for processing liquid fuel disposed at flow channel (26) for providing liquid fuel to heat engine, comprises a plurality of walls (50a, 50b) for applying magnetism arranged at an appropriate interval on the flow channel (26). As a surface of the walls (50a, 50b) is constituted at the upstream side of flow channel (26) from a south-pole magnet magnetized between 0.2 mT and 1.5 mT, south-pole magnetism can be efficiently applied to the liquid fuel, and combustion efficiency of heat engine of diesel vehicles, gasoline vehicles, LP gas-fueled vehicles, vessels, boilers etc. can be increased and all noxious substances in exhaust gas such as CO2, CO, HC. NOx, PM, etc can be considerably reduced.