An apparatus for controlling impedance in an adaptive tuning antenna circuit, said apparatus comprising: a coupler configured to output an inputted transmission signal to a transmission signal output terminal, to output a coupled power of the transmission signal to a coupling power output terminal and to output a reflected power to a reflected power output terminal; a tuner configured to control an impedance of an antenna and to supply the transmission signal outputted by the coupler to the antenna; a matching unit configured to be matched to the coupled power outputted by the coupler; a power detector configured to detect a level of the reflected power outputted by the coupler; and a controller configured to control an impedance of the matching unit by minimizing the level of reflected power detected by the power detector, and control the impedance of the antenna based on an impedance of the matching unit, characterized in that the matching unit comprises: a pin diode connected to the coupling power output terminal by an anode of the pin diode, and wherein an RF(Radio Frequency) impedance of the pin diode is changable by control of the controller, a varactor connected to the coupling power output terminal by a cathode of the varactor, connected in parallel to the pin diode, and wherein a capacitance of the varactor is changable by control of the controller, and an inductor connected in series to an anode of the varactor. a coupler configured to output an inputted transmission signal to a transmission signal output terminal, to output a coupled power of the transmission signal to a coupling power output terminal and to output a reflected power to a reflected power output terminal; a tuner configured to control an impedance of an antenna and to supply the transmission signal outputted by the coupler to the antenna; a matching unit configured to be matched to the coupled power outputted by the coupler; a power detector configured to detect a level of the reflected power outputted by the coupler; and a controller configured to control an impedance of the matching unit by minimizing the level of reflected power detected by the power detector, and control the impedance of the antenna based on an impedance of the matching unit, characterized in that the matching unit comprises: a pin diode connected to the coupling power output terminal by an anode of the pin diode, and wherein an RF(Radio Frequency) impedance of the pin diode is changable by control of the controller, a varactor connected to the coupling power output terminal by a cathode of the varactor, connected in parallel to the pin diode, and wherein a capacitance of the varactor is changable by control of the controller, and an inductor connected in series to an anode of the varactor. a pin diode connected to the coupling power output terminal by an anode of the pin diode, and wherein an RF(Radio Frequency) impedance of the pin diode is changable by control of the controller, a varactor connected to the coupling power output terminal by a cathode of the varactor, connected in parallel to the pin diode, and wherein a capacitance of the varactor is changable by control of the controller, and an inductor connected in series to an anode of the varactor.