A flame-retardant resin composition comprises (A) abase resin; (B) a flame retardant comprising (B1) at least one aromatic resin selected from a polyphenylene oxide-series resin and a polyphenylene sulfide-series resin, (B2) a phosphoric ester, and (B3) a nitrogen-containing cyclic compound; and (C) a styrenic resin having a melt flow rate of not more than 8 g/10 minutes. The base resin may be a polyester-series resin. The styrenic resin (C) may be a styrenic resin having a melt flow rate of 0.1 g/10 minutes to not more than 5 g/10 minutes. The phosphoric ester (B2) may be a condensed phosphoric ester, and the nitrogen-containing cyclic compound (B3) may be a polyphosphate of an amino group-containing triazine compound, a polyphosphoric acid amide, or others. The present invention provides a flame-retardant resin composition which has been flame-retarded without using a halogen-containing flame retardant.