The present description relates to a method for performing a HARQ process operation in a wireless communication system and to an apparatus using the method. A base station device which performs a HARQ process operation comprises a transmitter which transmits to a relay an uplink (UL) grant in a downlink backhaul subframe n which is a subframe having an index n among the allocated downlink backhaul subframes, and transmits, if downlink data sent from the relay in accordance with the uplink grant is not successfully received, a non-acknowledgement (NACK) signal in a downlink backhaul subframe n+N which is a downlink backhaul subframe that comes after N which is a predetermined number of HARQ processes counted from the downlink backhaul subframe n among the allocated downlink backhaul subframes.