To analyze traffic at an application level, a stream according to TCP or SCTP is required to be reconstructed and to be analyzed. When a packet is transferred to analyzing equipment using a port mirroring function with which a router and a switch are provided, transferred traffic volume increases and exceeds the throughput of the analyzing equipment. As only a part of packets configuring a stream is transferred to the analyzing equipment in transfer to the analyzing equipment using a packet sampling function, analysis at the application level is impossible. To solve the problem, when a packet communication unit recognizes a stream start packet, samples a stream initiated by the packet on a condition and at a rate respectively determined beforehand and generates a condition for copying the packet based upon information of both ends of the stream included in the packet, packets sampled in units of stream can be transferred to the analyzing equipment.