PURPOSE: To prolong peeling die's life for the purpose of improving the availability factor of equipment by giving ultrasonic vibration to a peeling die in the moving direction of a master wire.

CONSTITUTION: An ultrasonic device 17 is composed of the trembler 18 arranged surrounding the passage of a master wire 1, the horn 19 mechanically connecting the trembler 18 with a peeling die 7 to amplify the amplitude of ultrasonic vibration of the trembler 18 and conduct it to the peeling die 7, and a generator 20. From the generator 20 to the trembler is high-frequency current supplied. The master wire 1 is excited with the ultrasonic vibration conducted from the trembler 18 through the horn 19 in the moving direction of the master wire, and cutting resistance is pulsatively given by the die 7. Machinability is, therefore, improved, average cutting resistance decreases, and die's life is prolonged.