PURPOSE: To prevent the generation of a poor coiling shape, by controlling respective tensions of narrow steel strips obtained from the edge parts of a wide steel strip by looper drums, in coiling up the strips by a tension reel after longitudinally slitting the wide strip into plural lines of the narrow strips.

CONSTITUTION: A wide steel strip 25 is uncoiled from an uncoiler 23 and is longitudinally slit into plural narrow strips D1, D2, D3, D4 by a slitting device 20, and the strips are coiled up by a tension reel 21. In this case, because the thickness of each strip D1, D4 obtained from both edge parts of the strip 25 is smaller than that of each strip D2, D3 obtained from the central part of the strip 25, a slacking is generated at each strip D1, D4 while the strips are coiled, and that causes a poor coiling shape. Then, for preventing the slacking, looper drums 1A, 1B are attached to the lower parts of the strips D1, D4, and wire ropes 3A, 3B are lifted by tension winches 2A, 2B to make the tension of the strips D1, D4 equal to that of the strips D2, D3, thus the generation of the poor coiling shapes of the strips D1, D4 is prevented.