To provide an arc welding apparatus which can shorten a teaching time and perform tandem arc welding of high quality, and also to provide an arc welding apparatus with high quality and excellent operability.

In the arc welding apparatus, a first electrode 32 and a second electrode 42 of a torch 30 having consumable electrodes of welding wire are arranged in a designated direction to an object 60 to be welded while keeping a designated distance between the electrodes. The first electrode 32 performs welding and the second electrode 42 does welding succeedingly. A robot control unit 2 includes a tool dimension storing section 202 that stores relative positional relation between a tip of the first electrode 32 and that of the second electrode 42 taking a finger tip of the robot 1 as a reference, a locus calculation section 203 that calculates a locus of the robot 1 taking the tip of the first electrode 32 as the control point of the robot 1, and the second electrode position monitoring section 209 that calculates the tip position of the second electrode 42 and monitors a distance from welding start and welding end points to the position of the tip of the second electrode 42.