PURPOSE: To improve the dull life, by performing nitriding treatment the roll which is dull-treated by discharge.

CONSTITUTION: When the surface of rolling roll is dull-treated by discharge method austenite is left over on the outermost layer thereof. When nitrided at 500 to 600°C after discharge processing, the residual austenite is decomposed by heat, and nitride of high hardness deposites on the outermost layer. Thus, the dull life may be greatly increased, and dull unevenness may be eliminated. At the same time, formation of spalling on the roll surface layer may be prevented.