A melt-processable copolyester consisting essentially of:a structural unit (I) of formula (1-1) ##STR1## and formula (1-2) ##STR2## wherein the amount of the species of formula (1-2) is 5 to 95 mole % of the structural unit (I),a structural unit (II) of formula (2)--O--X--O-- (2)wherein X is at least one selected from the group consisting of ##STR3## and a structural unit (III) of formula (3)--O--Y--CO-- (3)wherein Y is at least one selected from the group consisting of ##STR4## the proportion of the structural unit (III) being 10 to 80 mole % of the structural units (I)+(II)+(III) in total, the structural unit (I) being substantially equimolar to the structural unit (II) and inherent viscosity (ln .eta..sub.rel)/C, measured in a concentration of 0.16 g/dl in pentafluorophenol at 60.degree. C., being not less than 0.5 dl/g.