A fuel reformer for reforming hydrocarbon base fuel into hydrogen rich gas, with one embodiment comprised of material containing at least 15 to 25% by mass Cr, 8 to 35% by mass Ni, 2 to 4% by mass Si and the remainder Fe and inevitable impurities (C, Mn, P, S or others). The material provides sigma brittleness resistance and cementation resistance, and provides a reformer that is lightweight, low-cost, highly reliable and durable. A second embodiment adds to the composition 0.05 to 1% by mass Nb, providing improved oxidation resistance, cementation resistance, intergranular corrosion resistance, with further improved reliability and durability.