A packet recovery method of the present invention is a packet recovery method upon loss of a plurality of packets transmitted from a first node 111 to second node 112 through a network in the order of sequence numbers assigned to each of said packets, wherein second node 112, upon detection of a loss of a packet transmitted from first node 111, transmits an acknowledgement message, including a sequence number of a packet whose receipt has been confirmed or whose loss has been detected and including information on the lost packet, to first node 111 through the network. Then, first node 111, upon receipt of the acknowledgement message from second node 112, assigns a sequence number that is different from that of any of the plurality of packets to a retransmission packet which is a packet to be retransmitted, and subsequently, transmits an acknowledgement-to-acknowledgement message attached to the retransmission packet through the network for notifying that the acknowledgement message has been received to second node 112.