PURPOSE: To prevent defective marking and to make marking clear and uniform by connecting a plasma arc torch with a plasma electric power supply and melting the surface of a stock to be marked by a plasma arc gas.

CONSTITUTION: The 1st pipe 14 for supply of a plasma gas and the 2nd pipes 17a and 17b for supply of cooling water are set inside a plasma arc torch 1 and an electrode 16 is adjacently placed to a spout hole 12 of a nozzle 13. The plasma gas supplied from the 1st pipe 14 is spouted into the atmosphere through a flow straightener 15. In that time, the plasma gas whose energy concentrates to the central part spouts when plasma arcs are generated between the electrode 16 and the nozzle 13. The marking is performed by melting the surface of a stock 7 to be marked by that gas. In that method, defective marking is eliminated and the marking is made to be clear and uniform because of no use of powders.