A polyester expressed by the following structural formula 1, and a charge transport material obtained by adding an electron acceptor compound or an electron donor compound to this polyester. ##STR00001## In the aforesaid structural formula, Ar is an aromatic group and this aromatic group may contain a heterocyclic ring.R.sup.1 is a carbon atom or absent (direct bond), R.sup.2 R.sup.9 are hydrogen atoms, electron donor groups or electron attracting groups, R.sup.20, R.sup.21 are hydrogen atoms or organic groups, X is a hetero atom, hetero atom-containing group, organic group or absent (direct bond), and m is an integer equal to 2 or more.