Abstract: A PCM communication apparatus including a plurality of channel units which receive input signal and a multiplexer unit which multiplexes signals. Each channel unit includes a digital conversion circuit which responds to an input signal by encoding the input signal and outputting the encoded signal and which responds to the absence of an input signal by outputting a predetermined encoded signal having zero-value bit positions. The channel unit further includes a code conversion circuit that inverts the bit positions of the signal output by the digital conversion circuit which correspond to the zero-value bit positions of the predetermined encoded signal and then outputs the converted signal.