PURPOSE: To superpose an analog signal to a PFM signal with a simple equipment and to reduce the cost of transmission by executing the PFM modulation of an analog signal and modulating the amplitude of another analog signal to form an analog superposed PFM signal on the transmission side, and on the reception side, demodulating the analog superposed PFM signal through a low-pass filter.
CONSTITUTION: When analog signals X, Y are inputted to a transmitter T, the analog signal X is PFM-modulated by a PFM modulation circuit 1 and applied to a amplifier 2 to obtain an analog superposed PFM signal whose envelope shape is the analog signal Y. When the analog superposed PFM signal is received by a receiver R, the sum signal of the analog signals X, Y is outputted from a low-pass filter 4. On the other hand, the PFM signal is identified at a prescribed threshold by an identifier 5 and the analog signal X is demodulated through a low-pass filter 6. The level of the demodulated analog signal X is adjusted by an amplifier 7 and the analog signal X is subtracted from said sum signal by a subtractor so that the analog signal X becomes '0' to obtain the analog signal Y.