TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: A raw solution before neutralization comprises alkali metal salt(s) (e.g. boric acid or phosphoric acid); or aluminum salt, titanium salt, calcium salt, strontium salt, barium salt, and/or boric acid. The complex compound may comprise phosphorus, boron, aluminum, titanium, calcium, strontium, and/or barium compound.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: Part or all of the hydroxyl groups of the polyvinyl alcohol domain are replaced by groups having a water absorption less than that of the hydroxyl group via acetalizing reaction, etherifying reaction, or esterifying reaction. The electrolyte may be produced by performing acetalizing reaction of aldehyde and solid electrolyte including complex compound under a condition of aldehyde and acid. The complex compound is produced by neutralizing alkali metal salt(s) (e.g. silicic acid, tungstic acid, molybdic acid, and/or stannic acid) by acid in the solution with polyvinyl alcohol coexisting or by neutralizing zirconium oxychloride by alkali in the solution with polyvinyl alcohol coexisting, and removing water as solvent. The solid electrolyte including the complex compound is subjected to heat-treatment at not less than 100degreesC or immersion treatment under acidic and/or alkali solution.Preferred Components: The aldehyde is n-butyric aldehyde, isobutyric aldehyde, and/or benzoic aldehyde.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: A raw solution before neutralization comprises alkali metal salt(s) (e.g. boric acid or phosphoric acid); or aluminum salt, titanium salt, calcium salt, strontium salt, barium salt, and/or boric acid. The complex compound may comprise phosphorus, boron, aluminum, titanium, calcium, strontium, and/or barium compound. EXAMPLE - An aqueous solution (30 cc, containing 7.5 wt.% sodium tungstate dihydrate and 3 wt.% trisodium phosphate) and an aqueous solution (10 cc, containing 3 wt.% sodium silicate) were added to a solution (100 cc, 10%) of polyvinyl alcohol having average polymerization degree of 3100-3900 and saponification degree of 86-90% to obtain raw solution. Hydrochloric acid solution 20 cc, 1.2 M) was dropped into the raw aqueous solution with agitation to obtain viscous precursor solution. The precursor solution was introduced into airtight container, evacuated by vacuum pump, to carry out defoaming. The defoamed precursor solution was cast on polyester film provided on smooth plate by heating the plate to 55-65degreesC. The cast solution was swept by a blade to smooth the solution into predetermined thickness. After fluidity of solution disappears, another solution was cast again, and swept by the blade. After repeating the process thrice, the plate was heated to 105-110degreesC for an hour. The resultant electrolytic film was stripped off from the plate, washed with water, and dried.