A transmission leakage signal offset apparatus of a radio frequency identification (RFID) reader is disclosed. The transmission leakage signal offset apparatus may include a signal divider to divide a received signal of the RFID reader, the received signal including a transmission leakage signal, and to transmit the divided received signal to a signal combiner and an injection locked oscillator (ILO); a signal synchronizer to synchronize a phase of the ILO with a phase of the transmission leakage signal; a phase controller to control a phase difference between the received signal of the RFID reader and an output signal of the ILO; and a signal combiner to combine the received signal of the RFID reader and the output signal of the ILO, between which the phase difference is controlled.