Abstract: A communication system has a Holter electrocardiograph having a biological signal detection apparatus having a transmitter 10 for processing and telemetering signals detected by a plurality of electrodes supported on supports for detecting biological signals, a receiver 14 for receiving the signal telemetered from the transmitter, demodulating the received signal, and outputting the demodulated signal to a biological signal input section of required record means, and a recorder 16 having record means for recording the demodulated signal by the receiver. The recorder of the Holter electrocardiograph has transmitting and receiving means 17 for telemetering the signal stored in the record means, receiving an external transmission signal, and telemetering some or all of the signals stored in the record means as instructed by the external transmission signal.