A melt-processable copolyester composed of the following structural units (I), (II) and (III) and/or (IV) as main structural components, whereinunit (I) is represented by the formula ##STR1## wherein X.sub.1, X.sub.2, X.sub.3 and X.sub.4, independently from each other, represent H, F, Cl, Br, CH.sub.3 or C(CH.sub.3).sub.3, provided that X.sub.1 to X.sub.4 do not simultaneously represent H, and n is 2 or 4,unit (II) is at least one unit selected from the group consisting of ##STR2## wherein at least one of the hydrogen atoms in each aromatic ring in units (II), (III) and (IV) may be substituted by an alkyl or alkoxy group having 1 to 4 carbon atoms or a halogen atom.The proportion of unit (I) is 2.5 to 35 mole %, the proportion of unit (II) is 2.5 to 35 mole %, and the proportion of unit (III), (IV) or a combination of units (III) and (IV) is 30 to 95 mole %.