To obtain a flame-retardant thermoplastic resin composition having good flame-retardancy and high heat-distortion temperature and impact strength by including a polycarbonate resin, a monovinylidene aromatic compound, a phosphoric acid ester flame-retarding compound and a specific amount of an acid scavenger.

The objective composition is produced by including (A) a polycarbonate resin, (B) a monovinylidene aromatic compound, (C) at least one kind of phosphoric acid ester flame-retarding compound, (D) an acid scavenger of an amount effective for keeping the increase of polycarbonate index to <50% after aging the resin composition for 6 weeks at 63°C and 100% RH and preferably further (E) a tetrafluoroethylene polymer. Preferably, the component D contains at least two molecular parts selected from epoxy, oxazoline and orthoester and is soluble in polycarbonate.