Disclosed is a flame-retardant epoxy resin composition characterized by containing (A) an epoxy resin containing 0.5-10 equivalent/kg of oxazolidone rings, (B) an epoxy group-containing phosphazene compound, (C) at least one compound selected from the group consisting of phosphates, condensed phosphates, quinone derivatives of phosphine compounds, and polyphenylene ethers, and (D) at least one curing agent selected from the group consisting of guanidine derivatives, phenol novolacs, bisphenol A novolacs, cresol novolacs and naphthol novolacs.