In arc welding in which a welding wire serving as a consumable electrode is fed toward a base material and a welding current is caused to flow through the welding wire and the base material to alternately repeat a reverse polarity period and a positive polarity period, after a short circuit between the welding wire and the base material is detected, a feeding speed of the welding wire is changed from a first feeding speed to a second feeding speed on a negative side of the first feeding speed when a speed in a direction toward the base material is defined as positive.