PURPOSE: To improve the anode conductivity of an electrolytic cell by forming the anode out of a Mn based perovskite type conductive oxide, which is obtained by partly replacing the La site of LaMnO3 with Sr, Mg or Ca, in a unit solid electrolyte type cell provided with the cathode on one surface of and the anode on the other surface of the solid electrolyte.

CONSTITUTION: This high temp. steam electrolytic cell comprises the unit solid electrolyte type cells, in each of which the tubular oxygen ion conductive solid electrolyte 2 is provided with the cathode 3 on its one surface and the anode 1 on the other surface. The above anode 1, namely the oxygen electrode consists of Mn based perovskite type conductive oxide which is formed by partly replacing the La site of LaMnO3 with an element selected from Sr, Mg and Ca in a ratio of 10 to 50mol%. In this cell, steam is electrolyzed to generate gaseous hydrogen and gaseous oxygen with the cathode 3, namely the steam side electrode. The gaseous oxygen thus generated is reduced by electrons to oxygen ions and the oxygen ions are diffused into the electrolyte 2 toward the anode 1 where electrons are released from the oxygen ions to convert the oxygen ions into gaseous oxygen.