An apparatus, a method and a relay system for removing self-interference (SI). If a relay transmitting end transmits relay-reference signals (R-RS) through a region where a base station does not transmit signals, based on a protocol predetermined with the base station, a relay receiving end obtains SI channel values from signals transmitted by the relay transmitting end and received through a self-interference channel with use of the R-RS, removes the SI from transmitting signals of an uplink or an downlink based on the SI channel values, and relays the SI removed transmitting signals.