Abstract: A flame-retardant synthetic resin composition comprising a thermoplastic resin selected from the group consisting of polyolefin, acrylonitrile-butadiene-styrene copolymer and ethylene-ethyl acrylate copolymer resins as a base polymer and, incorporated therein (A) a polyester fiber cut into a length smaller than 10 mm and/or a polyester powder having a particle size smaller than 10 mesh and (B) a polyphosphoric acid compound having a higher water resistance, wherein the amount of the thermoplastic resin is 40 to 95% by weight, the total amount of the components (A) and (B) is 5 to 60% by weight and the component (A)/component (B) weight ratio is in the range of from 5/1 to 1/20.