PURPOSE: To make it unnecessary to execute heat refreshing by impregnating NaOH in the pore part of a porous metallic oxide sintered body made of NmO, CuO, ZnO, Fe2O3 as raw materials.

CONSTITUTION: Materials MnO, ZnO, CuO, and Fe2O3 are mixed and roughly sintered and crushed to form Mn-Zn-Cu-Fe group metallic oxide powder whose grain size is ≤1μm. High molecular binder and dispersing agent are mixed and disepersed into the powder and the mixed/dispersed material is sintered as metallic oxide paste. Both the sides of the porous sintered product 1 are costed with silver paste, electrodes 2 are printed on both the coated sides and the electrode printed product is impregnated with NaOH solution of pH8 to 12 and then dried. Thus, the product can be improved to a change on standing of 3% RH after NaOH impregnation processing.