In order to preliminarily perform a load test or the like of an IP network, a test apparatus instructs a test packet transmitting device to transmit a test packet having a specified multicast address and instructs a test packet receiving device to receive the test packet of the multicast address. The test apparatus further instructs a first relay device to relay the test packet of the multicast address and instructs a second relay device to perform a route optimization excluding processing. The test packet receiving device requests the second relay device to transfer the test packet of the multicast address when the test packet receiving device has received the instruction to receive the test packet.