PURPOSE: To shorten the electrifying time and to save the consuming electric power by feeding a welding current by pressing a fixed pressure and by impressing an impact pressure to the electrode at the timing melted to certain degree.

CONSTITUTION: A fixed pressure is impressed on electrodes 2, 4 via a pressure cylinder 14 with the first switch 18 being closed by a start signal ST. On the other hand, a welding current I is fed to the electrodes 2, 4 with the welding delay time control part 44 starting the count of a synchronours pulse SP and closing the second switch 42 at the time of counting three pieces. An impact pressure delay time control part 52 impresses the impact pressure by closing the third switch 48 at the time of counting six pieces. The joining is therefore promoted, the welding time is reduced and the power consumption can be saved because of the impact being applied at the timing of the welding zone being melted to some degrees.