PURPOSE: To obtain an AM detector in which the fluctuation of a power supply voltage and the effect of a high frequency component are avoided by constituting the AM detector of a differenctial amplifier amplifying an input from an intermediate frequency amplifier circuit and a current synthesis circuit extracting a detecting signal.

CONSTITUTION: An output of the AM detector 50 is extracted from both collectors of transistors (TR)12,14 and is given to the AM detector 50. This AM detector 50 consists of the differential amplifier 52 converting a voltage of an intermediate frequency signal given from the intermediate frequency amplifier circuit 6 to a current, the current synthesis circuit 54 detecting the difference of currents flowing to amplifier elements constituting the amplifier 52, and an output circuit 56 converting the output current of the circuit 54 into a voltage. Through the constitution above, since the intermediate frequency signal is amplified by the amplifier 53 and the difference of currents flowing to TRs 58, 60 is used as a detecting signal, the fluctuation of the power supply voltage and the high frequency component are suppresesd as an in-phase component, thereby extracting the signal component only. As a result, a ripple eliminating characteristic and a noise eliminating characteristic are improved.