Nitrogen electrode reaction has been investigated in a LiBr-KBr-CsBr melt containing Li3N. The reaction N3- -> 1/2N(2) + 3e(-) is confirmed by quantitative analysis of anodically evolved gas. The Nernst relation holds for the rest potential of Ni electrodes at a nitrogen gas pressure, PN2, of 0.05-1.0 atm and an anion fraction of the N3- ions, x(N)(3-), of 0.003-0.010 (anion fraction). Then, the standard formal potential of the N-2/N3- couple, E-N2/N3-(o'), is evaluated to be 0.251 +/- 0.009 V versus Li+/Li (PN2 = 1 atm, x(N)(3-) = 1) at 673 K. The dependence of E-N2/N3-(o'), on the temperature (570-730 K) gives a linear relation, whose slope is (-0.930 +/- 0. 117) x 10(-3) V K-1. Thermodynamic quantities for the formation of Li3N in the melt are also estimated.