A fuel reforming device that prevents a flash-back phenomenon includes a reforming reactor and a heater. The reforming reactor reforms a fuel, and the heater provides thermal energy to the reforming reactor by generating the thermal energy by a catalytic oxidation reaction between a catalytic layer and an oxidation reaction material. The heater includes an inflow pipe that receives the oxidation reaction material, an outflow pipe that outputs a flue gas generated by the catalytic oxidation reaction, and a flue gas retrieving pipe that connects the outflow pipe and the inflow pipe to direct the flue gas to the inflow pipe.