To provide an in-line molding and filling system from the assembling of a paper tray and the molding of a plastic film to the filling with content in a process for manufacturing a paper container capable of being sufficiently hermetically sealed by a seal lid formed by integrating a molded plastic film with the inner surface of the paper tray based on paper and having flange.

The in-line molding and filling system, which uses the paper container formed by sucking a tray-shaped paper container main body based on paper and consisting of a flange part and a main body part and the inner surface protecting film layer comprising a thermoplastic resin on the inner surface of the paper container main body under vacuum or air pressure, consists of a preform part for assembling the paper container main body, a molding part for providing the inner surface protecting film layer to the inner surface of the paper container main body, a content filling part for filling the paper container with content, a lid sealing part for heat-sealing the seal lid to the paper container and a trimming part for cutting the outer periphery of the paper container.