Abstract: Aiming at achieving a fully improved effect of combustion efficiency and being durable for long-term use, a fuel reformer 1 of the present invention, typically disposed on a fuel supply path from a fuel tank of a vehicle to an engine, is configured so that a petroleum-derived liquid fuel reserved in the fuel tank of the vehicle is introduced through the fuel supply path and through an introduction port 52 into a cylindrical container 4, and and allowing it to modify with the aid of the first fuel-reforming grains 2, the second fuel-reforming grains 3 and permanent magnet 71. The engine supplied with thus-modified liquid fuel through the discharge port 53 raises effects of improving the combustion efficiency, improving the fuel cost, and reducing the emission gas.