To obtain a composition which can be kneaded with a resin in a good working environment and exhibits enhanced flame retardancy without deteriorating mechanical characteristics by incorporating, each in a specific amount, a non-halogen flame retardant compound and a novolak type phenol resin containing not more than a specific amount of free monomers and binuclear skeletal components with a polyester-based resin.

With 100 pts.wt. of a polyester-based resin (A) are incorporated 5-50 pts.wt. of a non-halogen flame retardant compound (B) selected among phosphorus-, nitrogen- and boron-containing compounds and 5-40 pts.wt. of a novolak type phenol resin (C) containing 5 wt.% or less of free monomers and binuclear skeletal components in total. As the component A is preferable a polybutylene terephthalate or a polyethylene terephthalate. As the component B there can be mentioned phosphorus-containing compounds such as phosphoric esters, acid phosphoric esters, condensed phosphoric esters, polyphosphate salts, elemental phosphorus and the like, nitrogen compounds such as melamine derivatives, guanidine derivatives and the like, and boron compounds such as zinc borate, boric acid, ammonium borate and the like.