Copolymerized polyester resin

The present invention relates to a copolymerized polyester resin wherein diethylene glycol and sodium sulfoisophthalate are copolymerized. The aim of the present invention is to solve the problem of die staining and foreign matter adhesion to products such as film, molded article, and fiber in the continuous production thereof; and the problem of resin coloring and reduction in molecular weight during recycling. According to the present invention, there is provided a copolymerized polyester resin containing dicarboxylic acid and glycol as constituting components, wherein the copolymerized polyester resin contains terephthalic acid as a main component of a dicarboxylic acid component, and contains ethylene glycol as a main component of a glycol component, wherein a content of terephthalic acid is from 80 to 94.95% by mole, a content of aliphatic acid having a carbon number of 2 to 4 is 5 to 20% by mole, and a content of sodium sulfoisophthalate is 0.05 to 10% by mole when a total amount of the whole dicarboxyl