PURPOSE: To accurately grasp an arc welding state and to monitor optional arc welding by detecting a welding current flowing through a welding electrode and base metal and determining the welding state or a welding result based on a moving average value of this welding current obtained by an arithmetic means.

CONSTITUTION: In a DC arc welding machine, the DC voltage is impressed on between the wedding electrode (welding wire) 14 at the welding torch 12 side from an arc welding power unit 10 and the base metal 16 and MIG welding or MAG welding is performed by a gas shielded arc welding process. During this arc welding, an arc voltage signal is inputted to a CPU28 via an A/D converter 20 from an output terminal of a voltage detection circuit 18. Meanwhile, a welding current signal is inputted to the CPU28 via an ADD converter 26 from an output terminal of a current detection circuit 24. This CPU28 carries out various operations and controls in this arc welding monitoring device by executing a program stored in a ROM32. Those variations can be elucidated clearly and in its turn, the arc welding state or the wedding result can be determined with high accuracy by obtaining the moving average for the welding current IC and the arc voltage EC during arc welding.