A loose-leaf binder device comprises a back, two end plugs that can selectively close two ends of the back, and a loose-leaf coil for binding inner pages and selectively disposed below the back. The back is formed with an insert slot. A retaining hole communicating with the insert slot is formed on a portion of the back abutting upon an end edge. The end plug is integrally formed with a resilient member to be inserted into the insert slot. A top surface of the resilient member is formed with one post corresponding to the retaining hole of the back. A free end of the resilient member is formed with an upward compressing edge. Thus, the post on the resilient member can be actuated through a compressing edge according to the resilient member of the end plug so that the post is selectively engaged with or disengaged from the back.