The flame-retardant adhesive composition contains a styrene-based elastomer containing a carboxyl group, an epoxy resin, and a phosphorus-containing oligomer including a structural unit represented by general formula (1), and the epoxy resin content is 1-20 parts by mass and the phosphorus-containing oligomer content is 10-50 parts by mass with respect to 100 parts by mass of the styrene-based elastomer containing carboxyl groups. (wherein, R1 and R2 are each independently a hydrogen atom or a methyl group, n is an integer of 1-20.)