The traffic load density measuring system includes a transmitter connected to a communication network for transmitting a packet, and a receiver for receiving the packet, in which a packet for load density detection is transmitted and received to measure a traffic load density within a predetermined transmission interval. The transmitter changes a transmission interval of the packet for load density detection, and adds transmission information capable of specifying a transmission time, a transmission interval, and a transmission number of the packet for load density detection to the packet for load density detection to transmit said packet. The receiver receives the packet for load density detection, extracts the transmission information from the packet for load density detection being received, and measures the load density within the predetermined transmission interval based on the extracted transmission information, and a delay or a lost status of the packet for load density detection.