To provide a technology for reducing loads of network devices such as routers and switches in a network system.

This invention provides a traffic monitoring system. The system is provided with: a transfer apparatus including a sampling apparatus; an off-load processing apparatus; and a traffic analysis apparatus. The sampling apparatus is provided with an extraction part for extracting transfer data from traffic on the basis of a preset standard and duplicating the extracted transfer data to generate sampling data and a capsulation processing part for executing capsulation processing for adding a header of which the destination is the off-load processing apparatus to the sampling data to generate capsuled data. The off-load processing apparatus generates flow data for analyzing the traffic in accordance with the capsuled data and transfers the flow data to the traffic analysis apparatus.