To provide an ultrafine cation-dyeable polyester multifilament combined filament yarn having different shrinkages and excellent softness, touch feeling, dyeability, color fastness, dynamic characteristics, and yarn manufacturing properties, and good combined filament processability, and to provide a fabric composed of the combined filament yarn.

A highly oriented undrawn polyester multifilament yarn is obtained as follows: The combined filament yarn having different shrinkages has a cation-dyeable polyester multifilament yarn as a low-shrinkable component. In the combined filament yarn having the different shrinkages, the cation-dyeable polyester multifilament yarn is composed of a modified polyester copolymerized with a specific sulfonic acid quaternary phosphonium salt and having an intrinsic viscosity of more than 0.6. The cation-dyeable polyester multifilament yarn has a dtex single filament fineness of not more than 0.7 and a birefringence (n) of 0.03 to 0.08.