To provide a polyester binder fiber with improved adhesiveness and a fiber structure containing the polyester binder. (1) A polyester binder fiber includes a polyester and a polymer having a repeating unit represented by the following formula (1) in a proportion of 0.1 to 5.0 mass % based on the mass of the polyester, and the polyester binder fiber has a crystallization temperature measured by differential calorimetry in a range of 100 to 250° C.; (2) a fiber structure includes the polyester binder fibers, and polyester subject fibers without a crystallization temperature, the polyester subject fibers being bonded via the polyester binder fiber. In the formula R1 and R2 are substituents each comprising arbitrary atoms chosen from C, H, N, O, S, P, and a halogen atom, the sum of the molecular weights of R1 and R2 is 40 or more, and n is a positive integer.