A packet analysis program that causes a computer to execute a process in a packet analysis system, wherein the packet analysis system comprises a relay device that relays a packet between a first communication device and a second communication device; a first switch provided in a transmission path between the first communication device and the relay device; a second switch provided in a transmission path between the second communication device and the relay device; and a packet analysis device coupled to the first and second switches (sw1, sw2), so as to acquire packets that flow through the relay device, the first communication device transmits a packet to the relay device via the first switch and the relay device relays and transmits the packet to the second communication device via the second switch, when the packet is received in a normal condition by the second communication device, the second communication device transmits an ACK to the relay device via the second switch and the relay device relays and transmits the ACK to the first communication device via the first switch, and the process comprises: acquiring, by the packet analysis device, a plurality of first delay times generated by a round trip of the packet from a time when the packet is captured through the second switch to a time when the ACK is captured through the second switch, and a plurality of second delay times generated by a round trip of the packet from a time when the packet is captured through the first switch to a time when the ACK is captured through the first switch; sorting separately the plurality of first delay times and the plurality of second delay times based on a length of a delay time; and calculating device delay times occurring in the relay device based on a first delay calculation that calculates a difference between each of the plurality of first delay times and each of the plurality of second delay times in a same rank after the sorting. the packet analysis system comprises a relay device that relays a packet between a first communication device and a second communication device; a first switch provided in a transmission path between the first communication device and the relay device; a second switch provided in a transmission path between the second communication device and the relay device; and a packet analysis device coupled to the first and second switches (sw1, sw2), so as to acquire packets that flow through the relay device, a relay device that relays a packet between a first communication device and a second communication device; a first switch provided in a transmission path between the first communication device and the relay device; a second switch provided in a transmission path between the second communication device and the relay device; and a packet analysis device coupled to the first and second switches (sw1, sw2), so as to acquire packets that flow through the relay device, the first communication device transmits a packet to the relay device via the first switch and the relay device relays and transmits the packet to the second communication device via the second switch, when the packet is received in a normal condition by the second communication device, the second communication device transmits an ACK to the relay device via the second switch and the relay device relays and transmits the ACK to the first communication device via the first switch, and the process comprises: acquiring, by the packet analysis device, a plurality of first delay times generated by a round trip of the packet from a time when the packet is captured through the second switch to a time when the ACK is captured through the second switch, and a plurality of second delay times generated by a round trip of the packet from a time when the packet is captured through the first switch to a time when the ACK is captured through the first switch; sorting separately the plurality of first delay times and the plurality of second delay times based on a length of a delay time; and calculating device delay times occurring in the relay device based on a first delay calculation that calculates a difference between each of the plurality of first delay times and each of the plurality of second delay times in a same rank after the sorting. acquiring, by the packet analysis device, a plurality of first delay times generated by a round trip of the packet from a time when the packet is captured through the second switch to a time when the ACK is captured through the second switch, and a plurality of second delay times generated by a round trip of the packet from a time when the packet is captured through the first switch to a time when the ACK is captured through the first switch; sorting separately the plurality of first delay times and the plurality of second delay times based on a length of a delay time; and calculating device delay times occurring in the relay device based on a first delay calculation that calculates a difference between each of the plurality of first delay times and each of the plurality of second delay times in a same rank after the sorting.