PURPOSE: To eliminate an asymmetric disturbing component by canceling by making use of the property of a symmetric side band characteristic to both side-band amplitude modulation system.

CONSTITUTION: The output of intermediate-frequency amplifying circuit 1 is supplied to the 1st synchronous detecting circuit 5 and the 2nd synchronous detecting circuit 6. Carrier extracting circuit 2 extracts a carrier from the output of circuit 1 and then supplies it to +π/2 phase shifter 3 and -π/2 phase shifter 4. A signal from phase shifter 3 is supplied to detecting circuit 6. As a result, A+π/4-phase- shifted signal appears at the output of detecting circuit 5, and a -π/4-phase-shifted signal at the output of detecting circuit 5, and that from phase shifter 4 to detecting circuit 6. The outputs of detecting circuits 5 and 6 are supplied to -π/4 phase shifter 7 and +π/4 phase shifter 8 respectively. The outputs of phase shifters 7 and 8 are both input to adding circuit 9. Adding circuit 9 obtains the sum of the outputs of phase shifters 7 and 8 and outputs an aural frequency signal.