PURPOSE: To carry out stable tension control at the time of winding and rewinding irrespective of set speed by transforming tension reference into the reference value of motor current, and giving this reference value of motor current to an A.C.motor.

CONSTITUTION: The output of an efficiency correction circuit 7 and an adjustable speed correction circuit 1 is inputted into a correction rate compensation circuit 8, and the inverse function of motor efficiency is integrated into a correction quantity by the correction rate compensation circuit 8 to compute the correction quantity responding to the number of revolutions of the motor, and the correction quantity is added to a tension-current substitution circuit 4 to form tension reference, which is transformed into the reference value of motor current by the tension-current substitution circuit 4, and the reference value of motor current is given through a speed-tension change-over circuit 5 and a polarity change-over circuit 6 to a A.C.motor. Thus since the correction in view of control is carried out to the variation of motor efficiency to make apparent motor efficiency within a variable speed range constant, stable tension control can be executed at the time of the winding and rewinding of a long sized material irrespective of set speed.