To provide a polyester which has no problem of coloration, excels in flame retardance, and can be applied to clothing fibers, industrial materials and the like.

The flame-retardant polyester comprises a polyester copolymerized with an organic phosphorus compound which has a phosphorus atom content of 500 to 15,000 ppm and 30-250 ppm magnesium compound on which a film layer composed of titanic acid is formed and has intrinsic viscosity of 0.55 or more and an L value in the Hunter's Lab colorimetric system of 50 or more, and its manufacturing method is described.