PURPOSE: To automatically adjust the tension of a tape by successively reducing the exciting current for a powder clutch by a prescribed value each time when the number of turns of a tape pad is reduced by a set number, in a tape winding machine for an electric cable, etc.

CONSTITUTION: The number P of pulses corresponding to the reduction by a prescribed number of turns is preset into a counter 34, and the number of pulses of a pulse generator 28 which should be generated for reducing the exciting current by a value (i) is set into a setting device 30, and a potentiometer 18 is adjusted so that the exciting current of a powder clutch 16 corresponds to the number of turns of a tape pad 10 before start. Then, operation is started, and each time when the value in the counter 34 reaches the set value P, a control output is transmitted into the pulse generator 28, and a stepping motor 24 is turned by a prescribed angle, and the exciting current of the powder clutch 16 is successively reduced by the value (i), and thus the tension of a tape can be adjusted automatically.