To provide a polyester combined filament yarn capable of producing woven or knitted fabrics capable of changing tough feelings by reversing core and sheath yarns of multifilament yarns by after processing

This polyester combined filament yarn comprises polyester multifilament yarn A and polyester multifilament yarn B simultaneously satisfying the following formulas: (1) 5≤BWS(A)-BWS(B)≤55, (2) 2≤HAS(B)-HAS (A)≤6, (3) BWS(B)≤15, (4) -5≤HAS(A)≤0, (5) 20×10-3≤Δn(A)≤60×10-3 and (6) 1≤Da≤5, wherein BWS(A) and BWS(B) are respective shrinkage factor (%) by boiling water of polyester multifilament yarns A and B; HAS(A) and HAS(B) are respective dry heat shrinkage factor (%) after heat treatment; Δn(A) is double refractive index of the above yarn and Da is single fiber fineness (dtex) of the above yarn A.