The present invention provides a digital communication system which is free from noise generated in a receiver. A transmitter converts an analog input signal to a digital signal, and then a power level detector 5 compares the digital signal with a predetermined level. In accordance with the result, the transmitter transmits a transmission signal which includes the digital signal or a digital signal amplified from that digital signal, and a control bit indicative of the result of comparison. The receiver, in accordance with the control bit included in the received digital signal, outputs an analog signal converted from the received digital signal or an analog signal converted from the received digital signal after it is digitally amplified.