A HARQ processing method is disclosed, by which a measurement gap is considered. In particular, as a terminal performs an inter-measurement operation, if HARQ feedback information reception is impossible, the terminal determines HARQ feedback information, which is not received for a next HARQ operation, as ACK or NACK by itself and is then able to perform the next HARQ operation. Specifically, in case that the terminal operates by determining the non-received HARQ feedback information as ACK, a corresponding uplink signal keeps being stored in an HARQ buffer and can be retransmitted according to a new UL grant reception from a base station.