The problem to be solved by the present invention is to provide a polyester binder fiber having a low crystallization temperature and exhibiting improved adhesiveness and a fiber structure including the polyester binder fiber. The polyester binder fiber according to the present invention includes a polyester polymer and an amorphous polyether imide polymer in a proportion of 0.1 to 5.0 mass % (based on the mass of the polyester polymer), and the polyester binder fiber has a crystallization temperature measured by differential calorimetry in a range of 100° C. or higher and 250° C. or lower.