Patented is a polyester pre-oriented conjugate fiber of either a side-by-side or an eccentric sheath/core configuration in which two kinds of polyester components are adhered to each other to form a single filament. At least one of the components consists of the single filament polytrimethylene terephthalate containing repeating units of trimethylene terephthalate of 90 mol % or more. The pre-oriented conjugate fiber is wound to form a package and satisfies the following items: a stretching elongation Vc prior to being treated with boiling water is less than 20%; an elongation at break is in a range from 60 to 120%; a dry heat shrinkage stress value is in a range from 0.01 to 0.15 cN/dtex; the difference in dry-heat shrinkage stress value between the conjugate fibers layered in the selvage portion and the central portion of the package is 0.05 cN/dtex or less; and a yarn fineness variation value U% is 1.5% or less and a variation coefficient of a yarn fineness variation period of 0.4 or less.