A packet flow monitoring device that monitors packet flow in a video or audio communication system constructed by an Ethernet (registered trademark) or IP (Internet Protocol) packet network, comprising: 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 some 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, wherein the extraction data report packet is composed of IP-format packets having a variable length within a range not exceeding a predetermined packet length, an IP header and a UDP header for performing transmission between the packet data extraction device and the extraction data aggregation device, an extraction data common header composed of items common to the aggregated, replicated passing packets, and packet-based extraction data composed of items individually extracted for the replicated passing packets are assigned to the extraction data report packet, and the packet-based extraction data is configured such that an extraction data individual header indicating information for identifying the extracted, replicated passing packets and extraction data that stores the some predetermined pieces of information in the extracted, replicated passing packets are paired with each other, wherein the extraction data common header includes a value indicating a reception time of beginning data of the replicated passing packet in each packet flow, the extraction data individual header includes a passing packet length indicating a length of the replicated passing packet, a data type indicating a packet type of the replicated passing packet, and elapsed time information indicating a temporal difference from the beginning data described in the extraction data common header, and the packet type includes a value that identifies at least Ethernet (registered trademark), IP, and RTP (Real-time Transport Protocol). 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 some 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, wherein the extraction data report packet is composed of IP-format packets having a variable length within a range not exceeding a predetermined packet length, an IP header and a UDP header for performing transmission between the packet data extraction device and the extraction data aggregation device, an extraction data common header composed of items common to the aggregated, replicated passing packets, and packet-based extraction data composed of items individually extracted for the replicated passing packets are assigned to the extraction data report packet, and the packet-based extraction data is configured such that an extraction data individual header indicating information for identifying the extracted, replicated passing packets and extraction data that stores the some predetermined pieces of information in the extracted, replicated passing packets are paired with each other, wherein an IP header and a UDP header for performing transmission between the packet data extraction device and the extraction data aggregation device, an extraction data common header composed of items common to the aggregated, replicated passing packets, and packet-based extraction data composed of items individually extracted for the replicated passing packets are assigned to the extraction data report packet, and the packet-based extraction data is configured such that an extraction data individual header indicating information for identifying the extracted, replicated passing packets and extraction data that stores the some predetermined pieces of information in the extracted, replicated passing packets are paired with each other, wherein the extraction data common header includes a value indicating a reception time of beginning data of the replicated passing packet in each packet flow, the extraction data individual header includes a passing packet length indicating a length of the replicated passing packet, a data type indicating a packet type of the replicated passing packet, and elapsed time information indicating a temporal difference from the beginning data described in the extraction data common header, and the packet type includes a value that identifies at least Ethernet (registered trademark), IP, and RTP (Real-time Transport Protocol).