To provide a flame-retarded synthetic resin composition having good flame retardance and improved weather resistance.

This composition is prepared by compounding (A) 100 pts.wt. synthetic resin with (B) 0.001-10 pts.wt. triazine light stabilizer represented by formula (1) (wherein R1 is a 1-17C alkyl; R2 is H or a 1-4C alkyl; and n is an integer of 1-20) and (C) 0.1-50 pts.wt. phosphorus flame retardant represented by formula (2) [wherein R3 to R7 are each a 1-10C alkyl or an aromatic group represented by formula (3) (wherein A1 and A2 are each H or a 1-10C alkyl; A3 to A8 are each H, a 1-4C alkyl, cycloalkyl, aryl, alkoxy, nitro, halogen, or cyano group; and B is a direct bond, -S-, a sulfonyl group or a 1-5C alkylidene or alkylene group); R5 is a divalent aromatic group represented by formula (4) or (5); and m is 0-30].