PURPOSE: To prevent roll marks from occurring and to improve the accuracy of flatness of a coil by unclamping work rolls before sizing feed is finished, backing the coil material by a specified distance after it is cut and sizing it.

CONSTITUTION: Before sizing feed of the coil material 1, the work rolls 4 are unclamped, compression to the coil material 1 is released and the coil material 1 is stopped when bending or stretching force has not acted on the coil material 1. After the coil material 1 has been stopped it is cut by a cutting machine to a specified size and at the same time that the cutting has been completed the coil material 1 is backed by a specified quantity. At the same time that the sizing feed is commenced to the coil material 1, the work rolls 4 are clamped, the coil material 1 is compressed, straightened and sized. Accordingly, the coil material 1 is not compressed while it stops, fed continuously all over the length and prevented from occurrence of roll marks.