A gateway apparatus includes a packet transmitting unit, duplicate packet detecting unit, and time measuring unit. The packet transmitting unit transmits to a counter apparatus the first packet that coincides with a packet transmitted immediately before reception of a delay measurement instruction for an IP (Internet Protocol) network between the gateway apparatus and the counter apparatus connected via the IP network. The duplicate packet detecting unit detects the second packet that is transmitted from the counter apparatus in response to reception of the first packet and coincides with a packet transmitted immediately before reception of the first packet. The time measuring unit measures the time until the duplicate packet detecting unit detects the second packet after the packet transmitting unit transmits the first packet. A communication system, delay measurement method, and recording medium are also disclosed.