A ball forming device and method used in a bonding apparatus, including a bonding arm, a capillary attached to the bonding arm, an electronic flame off prove for forming a ball at the tip of a wire passing through the capillary, and a gas atmosphere forming unit for bringing the vicinity of the tip end of the wire into a gas atmosphere. The gas atmosphere forming unit is made of an inner wall element and an outer wall element with a hollow space section in between. The bonding arm side of the inner wall element has an inside open space which is wider than the portion of the bonding arm where the capillary is attached, and gas ejection ports are formed in the inner wall element. A gas supply pipe is connected to the outer wall element to supply, for instance, a reducing gas into the hollow space section.