A filling device including a web-forming station (A), a filling station (B), a sampling station (C), and a retrieval station (D). A first box conveyor (3) for conveying boxes exiting a folder-gluer (1) and for forwarding them from the web-forming station (A) to the filling station (B) along a forwarding path (Ta). A second box conveyor (10) for conveying boxes forwarded by the first box conveyor (3) and for transferring them from the sampling station (C) to the retrieval station (D) along a transfer path (Tt).