To reduce the coefficient of friction and to decrease defects in end parts by supplying a lubricant to the web part of a material to be rolled, the web part and the root parts of flanges, the circumferential surfaces of upper and lower horizontal rolls or the circumferential surfaces and corner parts.

In a universal mill, the web part 11 is reduced with the horizontal rolls 6, 7 and the flange parts 12 are reduced between the side face parts of the horizontal rolls and the circumferential surface parts of vertical rolls. Slight difference in elongation between the flange parts 12 and the web part 11 is accumulated with the progress of rolling, it appears as a tongue or fish-tail shape in both end parts in the length direction of the material to be rolled and becomes defective parts. To reduce the coefficients of friction between the circumferential surfaces of the horizontal rolls 6, 7 and the web surfaces of the material to be rolled, or, in addition to them, between the corner parts of the horizontal rolls 6, 7 and the root parts of the web/flange of the material to be rolled, by supplying lubricating oil with lubricant jetting nozzles 16, the defective parts in the end parts of the material to be rolled are decreased and yield and production efficiency are improved.