TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Electrolyte: The electrolyte is alkali metal salt.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Electrolyte: The electrolyte is alkali metal salt.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Solvent: The organic solvent contained in the solid polymer electrolyte, has oxygen atom or nitrogen atom in the molecular structure.    TECHNOLOGY FOCUS - POLYMERS - Preferred Polymer: The organic polymer consists of homopolymer of vinylene carbonate group monomer having unit of formula (1), copolymer of vinylene carbonate group monomer and other monomer having unit of formula (2), homopolymer of carbonate group monomer having unit of formulae (3,5), or copolymer of carbonate group monomer and other monomer having unit of formulae (4,6). The organic polymer has mean molecular weight of 3x103-5x105 (preferably, 5x103-5x105). The organic polymer has carbonate group in side chain. The organic polymer is cross-linked mutually by diacryl or dimethacryl group monomer of formula (7), or trimethylol-propane tri(meth)acrylate of formula (9).R1-R3 of formulae (1-6)=hydrogen or lower alkyl;n,m,k of formulae (1-6)=arbitrary integers;X=copolymerizable monomer unit;j=0-3;R1,R2 of formula (7,9)=hydrogen or methyl;m=1-9;n=0-9;andCmH2m=linear or branched group, where a portion of (OcmH2m)n is substituted by formula (8).Preferred Composition: The solid polymer electrolyte contains 10-200 wt.pts (preferably, 10-400 wt.pts) of organic solvent with respect to 100 wt.pts of organic polymer. The ratio of vinylene carbonate group monomer unit or carbonate group monomer unit in organic polymer is 50 mol% or more. EXAMPLE - Vinylene carbonate (in g) (10) was mixed with azobisisobutyronitrile (4 mg), in a glass-made container that was substituted with nitrogen. The contents were solidified, de-aerated and nitrogen was introduced under vacuum. The polymerization reaction was carried out for 24 hours at 80degreesC. The viscosity of the reaction liquid was increased in between the polymerization reaction. After polymerization completion, the reaction material was cooled to room temperature. The obtained solid substance was dissolved in dimethyl formamide, and poured into methanol. Thus, fibrous white solid was obtained. The obtained solid was separated by filtration, washed with methanol, purified and dried. Thus, organic polymer (polyvinylene carbonate) was obtained in yield of 40%. The obtained polymer had mean molecular weight of 3x103-5x105 based on gel permeation chromatography. The obtained organic polymer was dissolved in dehydrated dimethyl formamide, to form a solution. The obtained solution was filtered, and formed into a film by casting method. Thus, polymer film was formed. The obtained polymer film was immersed into the electrolyte solution containing propylene carbonate (organic solvent) and lithium salt (LiClO4), to obtain solid polymer electrolyte film in which the organic polymer was swelled by the organic solvent. The obtained electrolyte film had high ion electric conductivity and flexibility.