In order to realize practical application of micro-plasma arc welding, the generation method of submillimetre-sized plasma arc was developed through controlling the DC electrical discharge in the range from glow to arc discharge with use of an experimental torch device and a newly designed high-voltage power source. The electrical discharge was established between the cathode of a tungsten electrode and the anode of stainless steel sheet through a plasma constriction nozzle made from heat-resistant material of boron nitride. It is shown that the micro-plasma arc with use of a submillimetre diameter nozzle is stabilized as the size of the plasma beam corresponds to the nozzle diameter and decrease in the nozzle diameter increases the power density of micro-plasma arc at the anode surface. A submillimetre-sized melt spot can be obtained with the current of 1 A and discharge time of 5 ms.