A curable composition for an adhesive agent, the curable composition comprising a polyorganosilsesquioxane comprising: a constituent unit represented by Formula: [R 1 SiO 3/2] where R 1 represents an ionic polymerizable functional group-containing group; a constituent unit represented by Formula: [R a SiO 3/2] where R a represents an ionic polymerizable functional group-containing group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, or a hydrogen atom; a constituent unit represented by Formula: [R b SiO 2/2 (OR c)] where R b represents an ionic polymerizable functional group-containing group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, or a hydrogen atom, and R c represents a hydrogen atom or an alkyl group having from 1 to 4 carbons; and a constituent unit represented by Formula: [R 1 SiO 2/2 (OR c)] where R 1 is synonymous with R 1 in Formula, and R c is synonymous with R c in Formula; wherein a molar ratio of the constituent unit represented by Formula to the constituent unit represented by Formula, [(the constituent unit represented by Formula)/(the constituent unit represented by Formula)], is from 20 to 500, a proportion of the constituent unit represented by Formula and the constituent unit represented by Formula is from 55 to 100 mol% relative to a total amount (100 mol%) of siloxane constituent units, a number average molecular weight is from 2500 to 50000, and a molecular weight dispersity, weight average molecular weight/number average molecular weight, is from 1.0 to 4.0, wherein the number average molecular weight and the molecular weight dispersity are measured by gel permeation chromatography in terms of polystyrene standard. a constituent unit represented by Formula: [R 1 SiO 3/2] where R 1 represents an ionic polymerizable functional group-containing group; a constituent unit represented by Formula: [R a SiO 3/2] where R a represents an ionic polymerizable functional group-containing group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, or a hydrogen atom; a constituent unit represented by Formula: [R b SiO 2/2 (OR c)] where R b represents an ionic polymerizable functional group-containing group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, or a hydrogen atom, and R c represents a hydrogen atom or an alkyl group having from 1 to 4 carbons; and a constituent unit represented by Formula: [R 1 SiO 2/2 (OR c)] where R 1 is synonymous with R 1 in Formula, and R c is synonymous with R c in Formula; wherein a molar ratio of the constituent unit represented by Formula to the constituent unit represented by Formula, [(the constituent unit represented by Formula)/(the constituent unit represented by Formula)], is from 20 to 500, a proportion of the constituent unit represented by Formula and the constituent unit represented by Formula is from 55 to 100 mol% relative to a total amount (100 mol%) of siloxane constituent units, a number average molecular weight is from 2500 to 50000, and a molecular weight dispersity, weight average molecular weight/number average molecular weight, is from 1.0 to 4.0, wherein the number average molecular weight and the molecular weight dispersity are measured by gel permeation chromatography in terms of polystyrene standard.