Method and device for synthesizing polyester

Provided are a method and a device that improve the starting material yield and simplify the wastewater treatment equipment in polybutylene succinate production. The method for producing polybutylene succinate is a method comprising an esterification step in which a starting slurry comprising succinic acid and 1,4-butanediol as the primary starting materials is subjected to esterification and an oligomer is synthesized, and a polycondensation step in which the oligomer is subjected to ester exchange, wherein a catalyst is added to the starting slurry during the esterification step, esterification is performed at 185 to 195°C, and additional catalyst is added during the polycondensation step.