In a large-scale backbone networks, the traffic monitoring system needs to receive a large volume of flow records, so if a single central collecting process is used, it might not be able to process all flow records. In this paper, we propose a method that achieves better scalability by using flow concentrators, which aggregate and distribute flow records. A flow concentrator is located between one or more routers and traffic collectors. The connection methods enable the number of flow concentrators to be adjusted to suit the size of a given network. We propose a reference model for a flow concentrator that is valuable for large-scale networks. We also evaluate the effectiveness of a flow concentrator developed based on these models and the effectiveness of the methods.