PURPOSE: To melt and squeeze the edge of a wire pin and to form a projected part in the radial direction, by thrusting the end of the wire pin fixed to an electrode to another electrode and applying current for a specified time.

CONSTITUTION: When a switch is turned on after a wire pin 34 is thrusted to an electrode 13, on-pulse of thyristors 38, 39 is outputted alternately from a switching controlling circuit 40 at every specified phase angle in positive and negative half cycles of power source AC waveform. Consequently, voltage is applied to the primary side of a transformer 37. Accordingly, if number of on-pulses of thyristors 38, 39 is determined beforehand, current flows to the wire pin 34 always for a fixed period and uniform finish can be obtained.