To provide polyester combined filament yarn capable of simultaneously fulfilling both requirements that it should have soft and voluminous feelings due to suitable puffiness and that it should have flame retardancy and durability of the flame retardancy, and to provide a woven/knitted fabric given by using the same.

This polyester combined filament yarn is composed of at least two kinds of polyester multifilament yarn threads, wherein a difference of yarn length between the kinds of the polyester filament yarn threads is not less than 10%, the multifilament yarn threads of the shortest yarn length have a resistance of incipient tension of 50-500 kg/mm2, and the multifilament yarn threads of the longest yarn length have an resistance of incipient tension of 500-850 kg/mm2.