PURPOSE: To improve the manipulation of strip-width control by making precise comparison between the contraction value of an input side and that of an output side by simultaneously recording measured values of width of the input side and output side of every advance of fixed distance of a strip.

CONSTITUTION: As strip 6 advances by the measuring place of input side width gauge 1, the number of pulses equivalent to the constant advance distance of strip 6 is counted by control computer 2 with pulses from pulse generator 12 and every time the count operation ends, the width is measured by input side width gauge 1 to store the measured value in control computer 2. When a measurement point at the measuring place of the input width gauge reaches the measuring place of outputside gauge 4, the number of pulses equivalent to the constant advance distance is counted by control computer 2 similarly as mentioned above. With regard to the current value, since the length between width gauges 1 and 4 on the input side and output side of strip 6 is calculated, this value is used as a character to retrieve the measured value of a reach to the position of current output side width gauge 4 and this value is output to recorder 3 simultaneously with the measured value of output side width gauge 4.