A flame-retardant resin composition comprises a thermoplastic resin; a flame retardant comprising a phosphorus-containing compound (A), a aromatic resin (B), and at least one flame-retardant auxiliary (C) selected from a nitrogen-containing compound and a metal salt of an inorganic acid; and at least one stabilizer auxiliary (D) selected from a compound having a functional group reactive to an active hydrogen atom and a water-repellent compound. The phosphorus-containing compound may be a phosphoric ester. The aromatic resin may be a polyphenylene sulfide-series resin or a polyphenylene oxide-series resin. The nitrogen-containing compound is a salt of an amino group-containing triazine compound with an oxygen acid, a salt of an amino group-containing triazine compound with a hydroxyl group-containing triazine compound, a polyphosphoric acid amide, a cyclic urea compound, or others. The present invention provides a flame-retardant resin composition which has been flame-retarded without using a halogen-containing flame retardant.