Abstract: Disclosed is a high-frequency signal detector circuit including a diode detector circuit for detecting an input signal by diode detection; a differential-input/differential output amplifier with a common mode feedback circuit, the amplifier including a differential amplifying circuit for differentially receiving outputs of the diode detector circuit and outputting a differential output signal, and a common mode feedback circuit for controlling the differential amplifying circuit in such a manner that a voltage corresponding to a mid-point of the differential output signal from the differential amplifying circuit will take on a voltage identical with a prescribed voltage; and a differential-input/single-ended output amplifier for receiving the differential output signal of the differential amplifying circuit and outputting a single-ended output signal.