A Cartesian feedback circuit comprising: a first loop filter circuit for limiting a signal band of a differential I signal, the differential I signal being a difference between a first I signal and a second I signal, the first I signal being an in-phase component of a modulated wave signal, the second I signal being an in-phase component of an amplified harmonic signal; a second loop filter circuit for limiting a signal band of a differential Q signal, the differential Q signal being a difference between a first Q signal and a second Q signal, the first Q signal being a quadrature-phase component of the modulated wave signal, the second Q signal being a quadrature-phase component of the harmonic signal; a quadrature modulator for generating a harmonic signal from the signal-band-limited differential I signal and the signal-band-limited differential Q signal; an amplifier for amplifying the harmonic signal generated by the quadrature modulator; a quadrature demodulator for demodulating each of the second I signal and the second Q signal from the harmonic signal amplified by the amplifier; a first inverse characteristic circuit having inverse frequency characteristics to frequency characteristics of the first loop filter circuit; and a second inverse characteristic circuit having inverse frequency characteristics to frequency characteristics of the second loop filter circuit, wherein the first I signal having passed through the first inverse characteristic circuit is outputted to the first loop filter circuit, and the first Q signal having passed through the second inverse characteristic circuit is outputted to the second loop filter circuit. a first loop filter circuit for limiting a signal band of a differential I signal, the differential I signal being a difference between a first I signal and a second I signal, the first I signal being an in-phase component of a modulated wave signal, the second I signal being an in-phase component of an amplified harmonic signal; a second loop filter circuit for limiting a signal band of a differential Q signal, the differential Q signal being a difference between a first Q signal and a second Q signal, the first Q signal being a quadrature-phase component of the modulated wave signal, the second Q signal being a quadrature-phase component of the harmonic signal; a quadrature modulator for generating a harmonic signal from the signal-band-limited differential I signal and the signal-band-limited differential Q signal; an amplifier for amplifying the harmonic signal generated by the quadrature modulator; a quadrature demodulator for demodulating each of the second I signal and the second Q signal from the harmonic signal amplified by the amplifier; a first inverse characteristic circuit having inverse frequency characteristics to frequency characteristics of the first loop filter circuit; and a second inverse characteristic circuit having inverse frequency characteristics to frequency characteristics of the second loop filter circuit, wherein the first I signal having passed through the first inverse characteristic circuit is outputted to the first loop filter circuit, and the first Q signal having passed through the second inverse characteristic circuit is outputted to the second loop filter circuit.