An object is to provide a plate-like partitioning wall allowing permeation of sodium ions therethrough and having high safety and durability. A plate-like partitioning wall 2 of the present invention is formed from a solid electrolyte allowing permeation of sodium ions therethrough. The plate-like partitioning wall 2 has a plate-like shape having, in a center part in the thickness direction thereof, a negative electrode chamber 20 to which molten sodium is supplied. This negative electrode chamber 20 is formed as a foil-like space extending in two-dimensional directions or as a pore-like space extending in two-dimensional directions in a net-like shape. The negative electrode chamber 20 of this plate-like partitioning wall 2 is formed as a thin foil-like space or as a fine pore-like space, and thus, the amount of molten sodium stored therein is very small. Therefore, even when this plate-like partitioning wall 2 is broken and reaction with molten sulfur occurs, the amount of heat generation is small, ignition is not caused, and thus, safety is high. The burn-out pattern and the organic matter powder forming the negative electrode chamber may also be those that are thin or fine. Thus, a small crack or the like is less likely to occur in the compacted body, and durability of the plate-like partitioning wall is high and manufacture thereof is facilitated.