PURPOSE: To easily detect the slip of the pinch roll, by counting the output of the pulse oscillator installed in the coiler since the material passes over the rolling mill, and by operating the circumferential speed of the coil from this count value, and by comparting this circumferential speed with the speed of the pinch roll.

CONSTITUTION: The input selector 8 selects the pulse oscillator 6 for the pinch roll since the rolled material passes over the rolling mill. The outut of the divider 11 is connected to the preset-up-counter 12 whose another terminal is connected to the pulse oscillator 7 for the coiler. The number of pulse counted by the counter 12 indicates the quantity proportional to the coil diameter of the coiler every moment. This output is inputted to a terminal of the multiplier 13, and to another terminal is inputted the r. p. m. of the coiler; hereby, the circumferential speed of the coil, that is the speed of the rolled material, is obtained. This speed of the rolled material together with the speed of the pinch roll are inputted to the comparator 14; from the difference obtained from this comparison, the slip of the pinch roll is detected. This output is given to the controller on purpose to synchronize the speed of the pinch roll with the speed of the rolled material.