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 forumla R 1 and R 2 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 R 1 and R 2 is 40 or more, and n is a positive integer.