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Torsional Vibration between Metal Rolling Rolls and a Rolling Mill Motor, may occur in recent days, as a result of higher speed response adjustment for variable speed rolling mill motor drive system. Therefore online transfer function analysis, in which white noise signal is superposed to speed reference signal in between real rolling operation, is applied to the variable speed rolling mill motor drive system, in order to realize both higher response adjustment and avoiding the motor shaft torsional resonance, at the same time. Issues in this paper are focused on excess acceleration value, in tangential direction of the mill motor rotor, which is caused by the motor shaft torsional resonance at the white noise signal superposition to the speed reference signal of the motor drive system for the online transfer function analysis. As a result of the acceleration analysis, the acceleration values in "G" (Relative acceleration value on the basis of Gravity) can be plotted on "Bode-Diagram", which is namely frequency response for the speed signal amplitude transmission ratio. In addition, relation between the white noise amplitude reduction and the transfer function analysis accuracy deterioration is also examined, in this paper. The smaller the white noise amplitude be, the larger the analysis error will be, due to resolution reduction by the smaller white noise signal amplitude.