With the development of semiconductor devices, adoption of microcontroller prevails in industrial area. But in are welding industry, there has not been much progress in adoption of microcontroller technology. Therefore, this paper shows the application of digital control technology to welding machine. This paper presents the design of microcontroller that is appropriate for three phase $CO_2$ gas metal are welding machine. By using microcontroller in $CO_2$ gas metal are welding machine, the overall cost can be reduced compared to analog comtroller. Also TMS370C850 microprocessor is used as overall microcontroller for the are welding machine.