NOVELTY - The ferritic stainless steel comprises (in mass%) chromium (12-20), carbon (0.03 or less), nitrogen (0.03 or less), silicon (0.1-1.5), manganese (0.1-1.5), sulfur (0.008 or less), aluminum (1.5 or less) and niobium (0.1-0.8), titanium (0.03-0.5), molybdenum (0.1-4) and/or copper (0.1-4), and remaining iron. The amount of chromium, manganese, aluminum and silicon satisfies a preset relation.    USE - As structural material of modifier which generates hydrogen by modification reaction of hydrocarbon group fuel.    ADVANTAGE - The ferritic stainless steel has improved high temperature strength and thermal fatigue property imparted by predetermined amount of niobium, titanium, molybdenum and copper. Weldability, workability and low temperature roughness are improved by additional amount of chromium, silicon and aluminum. Sufficient durability is exhibited as structural material of modifier even when exposed to lot of water vapor, carbon monoxide and high temperature atmosphere containing carbon dioxide. The water vapor oxidation and red scale production is avoided, and steam reformation of hydrocarbon fuel is carried out at stable conditions. Chromium imparts corrosion resistance and oxidation resistance, carbonitride imparts water vapor resistance and red proof scale property and silicon effectively improves the environmental crossing gate ability of oxide film.    DETAILED DESCRIPTION - The ferritic stainless steel comprises (in mass%) chromium (12-20), carbon (0.03 or less), nitrogen (0.03 or less), silicon (0.1-1.5), manganese (0.1-1.5), sulfur (0.008 or less), aluminum (1.5 or less) and niobium (0.1-0.8), titanium (0.03-0.5), molybdenum (0.1-4) and/or copper (0.1-4) and remaining iron. The amount of chromium, manganese, aluminum and silicon satisfies the following relation: A=Cr+Mn+5(Si+Al) and is equal to 15-25.    DESCRIPTION OF DRAWING(S) - The figure shows sectional drawing of hydrocarbon group fuel modifier. (Drawing includes non-English language text).