The present invention is directed to reducing leakage of a transmitting signal to a receiving unit in a wireless communication system with a transmitting unit and the receiving unit sharing an antenna. A coupling apparatus for dividing a radio frequency (RF) transmitting signal and an RF receiving signal in a transceiver with a transmitting unit and a receiving unit sharing an antenna, includes: a four-port circuit having port 1, port 2, port 3, and port 4, a through path being formed between the port 1 and the port 2, a first signal input to the port 1 being coupled to the port 4, a second signal input to the port 2 being coupled to the port 3, and an isolation path being formed between the port 1 and the port 4 and between the port 2 and the port 3; and an attenuator attenuating and outputting a signal output from the port 3 of the four-port circuit, and the RF transmitting signal is input to the port 1 of the four-port circuit, the RF receiving signal is input to the port 2 of the four-port circuit, and outputs of the attenuator and the port 4 of the four-port circuit are provided the receiving unit. Leakage of a transmitting signal of a transmitting unit to a receiving unit in a communication system sharing an antenna can be isolated. Furthermore, an isolation effect of a leakage signal of a transmitting unit to a receiving unit can be maximized while adaptively changing an attenuation value of a variable attenuator.