A square detection circuit square-detects a portion of a high frequency transmission signal that is extracted by a directional coupler, of a high frequency transmission signal amplified by a power amplifier. A first adjustment circuit extracts a DC component from a detection output of the square detection circuit, and adjusts respective amplitudes of baseband I and Q signals generated by an I/Q signal generation circuit, in response to the extracted DC component. A second adjustment circuit extracts an AC component from the detection output of the square detection circuit, and adjusts the respective amplitudes and phases, and the respective DC offsets of the baseband I and Q signals generated by the I/Q signal generation circuit, in response to the extracted AC component.