Electrochemical reduction of nitrogen gas in the molten LiCI-KCl system has been studied by electrochemical measurements combined with gas analysis using a nitrogen gas electrode. It was found that nitrogen gas was electrochemically reduced to produce nitride ions almost quantitatively according to the following reaction : 1/2N(2) + 3e(-) = N3-. It was confirmed that the use of a nitrogen gas electrode as counter electrode allows us to supply nitride ions successively during anodic surface nitriding in LiCl-KCl systems.