To provide a copolyester polymer having excellent dyeing property with a cation dye and flame retardance, and a method for manufacturing the same.

The flame retardant cationically dyeable copolyester polymer includes a metal sulfonate-containing compound by 0.5 to 3 mol% based on the content of the carboxylic acid residue over the entire part of the polymer, and a phosphorous flame retardant by 500 to 50,000 ppm based on the content of the polymer with a phosphorus atom as a reference. The flame-retardant cationically dyeable copolyester polymer is manufactured at a low manufacturing cost by using a TPA (terephthalic acid) polymerization method.