PURPOSE: To simplify the circuit constitution by providing a quadrature detecting circuit in a stereophonic receiver of amplitude modulation (AM).

CONSTITUTION: A high-frequency signal of frequency modulation is converted into an intermediate-frequency signal, the high-frequency signal of amplitude modulation is converted (5) into an intermediate-frequency signal, and each signal is inputted to the quadrature detecting circuit 3 via a capacitor C1 and each signal is integrated. An output of the quadrature detecting circuit 3 at the reception of the frequency modulation high-frequency signal is received and separated at a multiplexer 4 for left and right sound signal of a stereophonic reproducing sound. An output of the quadrature detecting circuit 3 at the reception of the amplitude modulation high-frequency signal and a detecting signal 3 are received and separated into the left/right sound signal of stereophonic reproducing sound at a decoder circuit 9.