PURPOSE: Liquid fuel is allowed to pass through a device where the fuel can come into direct and indirect contact with magnets to increase the magnetization efficiency, permit the long-time stay of the fuel in the casing and regulate the Gauss by changing the feed rate.

CONSTITUTION: The fuel from the inlet 5 is increased in its contact area with the magnets by passing it between granules and particles of magnets to effect direct magnetization sufficiently. Further, the resultant fuel is passed through the gaps between the ferromagnetic plates 4 and the inner walls of the casing, then through the magnet layers 3 to effect the repitition of magnetization. Finally the fuel is led into the pipe 2 to effect indirect magnetization and made to flow out of the outlet 6 whereby the liquid fuel is subjected to magnetization treatment to increase its combustion efficiency.