PURPOSE: To reduce the amount of cut-down in the tip and tail end parts and to improve yield by exactly controlling width of a sheet in the tip and tail end parts of a rolling material while preventing width drop.

CONSTITUTION: Edger rolls 3 for controlling the width in the tip and tail end parts of the rolling stock 1 at a prescribed pitch in the longitudinal direction of the rolling stock 1 in a rolling device are provided. After respectively independently determining the opening degrees of edger at respective control points at each ΔL [mm] in the longitudinal direction of the rolling stock based on actual values S1 collected from an edger inlet-side width meter 6 which is provided on the inlet side of the edger rolls 3, whether those values are achievable or not from the viewpoint of the capacity of the oil column of edger is checked and the opening degree of edger is corrected so as to be achievable with an arithmetic unit 10 for the opening degree of edger.