PURPOSE: To simplify moving function by using a torsion bar as a driver for driving a ball forming means toward/from the tip of a wire.

CONSTITUTION: To permit a discharge electrode 14a to approach a wire 8, an electromagnet 13 is turned ON to have a work piece 13b of the electromagnet 13 moved toward a main body 13a so as to swing a lever 12 together with a torsion bar 11 in the direction A around the core of the torsion bar 11. Thus the discharge electrode 14a approaches the tip of the wire 8 to face it. By applying high voltage between the two, discharge is generated between the tip of the wire 8 and the discharge electrode 14a to form a ball at the tip of the wire 8. After the ball is formed, voltage application is stopped and the electromagnet 13 is turned OFF in order to separate the discharge electrode 14a from the wire 8. When the electromagnet 13 is turned OFF, the torsion bar 11 functions to move the lever 12 in the direction B for releasing the twisting force and the discharge electrode 14a moves off the wire 8, Thus, a driving mechanism of a ball forming means is simplified and a highly reliable device is obtained.