To detect the communication conditions of a communication path set in a packet network such as a VoIP network, a detection packet is periodically transmitted to the communication path and a load packet is transmitted to the communication path. Then, the time and loss conditions regarding a detection packet having passed through the communication path are detected, and changes in delay and jitter conditions and changes in loss rate according to a traffic load are grasped. Changes in the communication conditions of the communication path at high load can be detected while minimizing the occurrence of adverse effects on other communications.