Abstract: A method and apparatus for arc welding particularly regarding a pulse arc welding machine comprising a welding power source having an output characteristic control circuit, an overload protection circuit, a driving circuit, and a main power circuit, and a wire feeding unit having a wire feeding control circuit, a motor driving circuit and a wire feed motor. The output characteristic control circuit comprises a welding arc autoregulating control system which provides the power source with a multi-segmental and moving output characteristic with varying slope, a circuit for connecting arbitrary number of output characteristic segments with arbitrary or varying slope, and a scanning circuit for obtaining the output characteristic segment with varying slope. A particular use of the control system is in an easy to operate autoregulating controlled GMA welding machine with one-knob control of wire feed rate without having to adjust the other welding parameters.