PURPOSE: To facilitate the tuning of an AM receiver, by applying the quadrature wave detection of an FM receiver to the AM receiver, and displaying the state of the detection to a tuning meter synchronously.

CONSTITUTION: The output signal supplied from a frequency converting circuit consisting of a mixing circuit 5 and a local oscillator 11 of an AM receiver is fed to an IF amplifier 12 of an FM receiver. The output signal of the amplifier 12 is fed to a quadrature wave detector 13 and a quadrature limiter 15. A phase shifter 16 is switched by a switch SW between the AM and FM waves. The output of the shifter 16 is fed to the detector 13 and then compared with the input signal given from the amplifier 12. A turning coil 17 is connected so as to give an input to the detector 13. The output of the detector 13 is displayed in tuning to a tuning meter of a tuning meter circuit 18 via a tuning meter driving circuit 14.