A packet flow monitoring device, a packet data extraction device, an extraction data aggregation device, and a program for efficiently and highly accurately monitoring a packet flow in a video or audio communication system constructed by an Ethernet (registered trademark) frame or IP packet network. This packet flow monitoring device includes: a packet data extraction device that replicates all passing packets that pass through one or a plurality of specific network switches on the network and extracts and aggregates some predetermined pieces of information in the replicated passing packets to form and output an extraction data report packet; and an extraction data aggregation device that receives the extraction data report packet, analyzes the extraction data report packet so as to aggregate the predetermined pieces of information in the replicated passing packets included in the extraction data report packet for each packet flow, and records the aggregated information as aggregation data.