A gel electrolyte for a lithium ion secondary battery, comprising: a lithium salt; a copolymer of a monomer represented by the following formula or and a monomer represented by the following formula; a compound having a phosphazene structure represented by the following formula; and as an additive, at least one compound selected from a cyclic disulfonate ester represented by the following formula, and a chain disulfonate ester represented by the following formula: wherein in the formula, R 1 denotes H or CH 3; and in the formulas and, R 2 denotes one of substituents represented by the following formula; wherein in the formula, R 3 denotes an alkyl group having 1 to 6 carbon atoms; wherein in the formula, R 4 denotes H or CH 3; R 5 denotes -COOCH 3, -COOC 2 H 5, -COOC 3 H 7, -COOC 4 H 9, -COOCH 2 CH(CH 3) 2, -COO(CH 2 CH 2 O) m CH 3, -COO(CH 2 CH 2 O) m C 4 H 9, -COO(CH 2 CH 2 CH 2 O) m CH 3, -COO(CH 2 CH(CH 3)O) m CH 3, -COO(CH 2 CH(CH 3)O) m C 2 H 5, -OCOCH 3, -OCOC 2 H 5, or -CH 2 OC 2 H 5; and m denotes an integer of 1 to 3; wherein in the formula, X 1 and X 2 each independently denote a halogen element or a monovalent substituent; the monovalent substituent denotes an alkyl group, an alkoxy group, an aryl group, an acyl group, an aryloxy group, an amino group, an alkylthio group, an arylthio group, a halogenated alkyl group, a halogenated alkoxy group, a halogenated aryl group, a halogenated acyl group, a halogenated aryloxy group, a halogenated amino group, a halogenated alkylthio group, or a halogenated arylthio group; n denotes an integer of 3 to 5; and the formula may be cyclic; wherein in the formula, Q denotes an oxygen atom, a methylene group or a single bond; A 1 denotes a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms which may be branched, a carbonyl group, a sulfinyl group, a substituted or unsubstituted perfluoroalkylene group having 1 to 5 carbon atoms which may be branched, a substituted or unsubstituted fluoroalkylene group having 2 to 6 carbon atoms which may be branched, a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms which contains an ether bond and may be branched, a substituted or unsubstituted perfluoroalkylene group having 1 to 6 carbon atoms which contains an ether bond and may be branched, or a substituted or unsubstituted fluoroalkylene group having 2 to 6 carbon atoms which contains an ether bond and may be branched; and A 2 denotes a substituted or unsubstituted alkylene group which may be branched; or wherein the compound of formula is selected from compounds 6, 11, 14 and 21 shown in Table 1; wherein in the formula, R 6 and R 9 each independently denote an atom or a group selected from a hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 5 carbon atoms, a substituted or unsubstituted fluoroalkyl group having 1 to 5 carbon atoms, a polyfluoroalkyl group having 1 to 5 carbon atoms, -SO 2 X 3 (wherein X 3 is a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), -SY 1 (wherein Y 1 is a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), -COZ (wherein Z is a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), and a halogen atom; and R 7 and R 8 each independently denote an atom or a group selected from a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 5 carbon atoms, a substituted or unsubstituted phenoxy group, a substituted or unsubstituted fluoroalkyl group having 1 to 5 carbon atoms, a polyfluoroalkyl group having 1 to 5 carbon atoms, a substituted or unsubstituted fluoroalkoxy group having 1 to 5 carbon atoms, a polyfluoroalkoxy group having 1 to 5 carbon atoms, a hydroxyl group, a halogen atom, -NX 4 X 5 (wherein X 4 and X 5 are each independently a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), and - NY 2 CONY 3 Y 4 (wherein Y 2 to Y 4 are each independently a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms). a lithium salt; a copolymer of a monomer represented by the following formula or and a monomer represented by the following formula; a compound having a phosphazene structure represented by the following formula; and as an additive, at least one compound selected from a cyclic disulfonate ester represented by the following formula, and a chain disulfonate ester represented by the following formula: wherein in the formula, R 1 denotes H or CH 3; and in the formulas and, R 2 denotes one of substituents represented by the following formula; wherein in the formula, R 3 denotes an alkyl group having 1 to 6 carbon atoms; wherein in the formula, R 4 denotes H or CH 3; R 5 denotes -COOCH 3, -COOC 2 H 5, -COOC 3 H 7, -COOC 4 H 9, -COOCH 2 CH(CH 3) 2, -COO(CH 2 CH 2 O) m CH 3, -COO(CH 2 CH 2 O) m C 4 H 9, -COO(CH 2 CH 2 CH 2 O) m CH 3, -COO(CH 2 CH(CH 3)O) m CH 3, -COO(CH 2 CH(CH 3)O) m C 2 H 5, -OCOCH 3, -OCOC 2 H 5, or -CH 2 OC 2 H 5; and m denotes an integer of 1 to 3;