Provided are: a polyester-based resin composition that has excellent incombustibility and melt thermal stability and is also superior in laser printability; and a production method for same. The present invention pertains to: a polyester-based resin composition that contains 3-60 parts by mass of a brominated polyacrylate-based flame retardant (B) with respect to 100 parts by mass of a thermoplastic polyester resin (A), and that is characterized in that the brominated polyacrylate-based flame retardant (B) has a Na element concentration of 5-4000 ppm as measured by fluorescent X-ray spectroscopy; and a production method characterized by comprising rinsing the brominated polyacrylate-based flame retardant (B) with heated water having a temperature of 40-100°C, and then drying the rinsed product and mixing the dried product with the thermoplastic polyester resin (A).