To provide an ordinary-pressure cationically dyable polyester which can be cationically dyed at ordinary pressure, has good hue, and has a high degree of polymerization.

The polyester is a copolymerized polyester constituted of ethylene terephthalate as a main repeating unit. The copolymerization is performed such that a sulfoisophthalic acid metal salt and a sulfoisophthalic acid ammonium or phosphonium salt satisfy specific mathematical formulae. The copolymerized polyester includes a reaction product of a titanium compound and a specific phosphorus compound, elementary antimony, and an elementary alkaline earth metal so as to satisfy specific mathematical formulae.