The present invention provides a polyester resin component having crystallization improved and including a cyclic compound shown by a below-described formula and polyester capable of having a crystal structure. ##STR00001## (In the formula, a ring A and a ring B respectively represent benzene rings, and hydrogen bonded to the benzene rings may optionally be substituted with other groups. Y represents --CONH-- or --NHCO--. X represents a heterocyclic group or a condensed heterocyclic group including one or more NH or CO respectively).