PURPOSE: To obtain a polyester multifilament yarn having worsted fabric-like soft swelling feeling, free from shiner, deeply dyeable and suitable for heavy- gage woven and knitted fabric.

CONSTITUTION: The objective specific combined filament yarn of polyester is characterized in that the yarn is combined filament yarn consisting of at least three kinds of polyester multifilaments of high shrinkage yarn, middle shrinkage yarn and low shrinkage yarn which are different in boiling point shrinkage and these polyester multifilament satisfy the following conditions (a) to (c) and the high shrinkage yarn and the middle shrinkage yarn form the core part in combined state and the low shrinkage yarn forms the sheath part and 20-60/m interlacing is applied to whole the combined filament yarn. (a) Boiling water shrinkage of high shrinkage yarn is 40-15% and boiling water shrinkage of middle shrinkage yarn is 20-8% and boiling water shrinkage of low shrinkage yarn is 15-5%, (b) at least high shrinkage yarn is triangular to heptagonal modified cross-section yarn and (c) low shrinkage yarn is a non- modified cross section yarn spun and wound at a rate of ≥3500m/min and having 0.05-0.12 birefringence index (Δn) and 70-20g/d Young's modulus.