Abstract: A method and apparatus for determining the stability of arc welding between a base metal and a welding electrode. A welding current for the arc period and a welding current for the short-circuit period fed from a welding power source are sampled every cycle of the repetition of arc and short-circuit, in accordance with a predetermined sampling frequency. The welding current for the arc period is integrated, and a standard deviation of the integrated welding current for the arc period is calculated. The standard deviation of the integrated welding current for the short-circuit period is calculated, as well. These standard deviations are multiplied together to produce a product, so that a welding stability parameter is calculated on the basis of the product. Then, the welding stability parameter is compared with a predetermined reference value. In response to the result of comparison, the welding stability between the base metal and the welding electrode is determined.