Provided a method and device for efficiently retransmitting packets of which transmissions failed in wired/wireless network including detecting continuity by detecting whether or not a sequence ID of a received packet is continuous with a start sequence ID or an end sequence ID of packets included in reception blocks which are generated in advance of the received packet; depending on the result of the detection, manipulating reception blocks to renew or delete the reception blocks or generate a new reception block by using the sequence ID of the received packet; and transmitting an EBN (Explicit Block NACK) for requesting retransmission of lost packets in units of a block when discontinuity is detected.