A small amount of NO pulse-injected into a Rowing He gas was reduced using the combination of a zirconia oxygen pump-gauge and a potentiostat. Its performance was evaluated from the amount of NO which was reduced electrochemically by the oxygen pump and that was decomposed chemically. The electrochemically stimulated decomposition of NO proceeded by removing the generated oxygen through the oxygen pump. The electrochemical reduction of NO proceeded to a greater extent at lower pump potentials and was complete when the pump potential was maintained at -500 mV and below. The pump-gauge responded quickly in both one pulse and intermittent pulse injections. It is confirmed from a hydrodynamical standpoint that the pump-gauge with a straight and fine zirconia tube is useful in intelligently controlling reduction and oxidation of gases and in evaluating their redox activities.