Abstract: A bidirectional communication system 1 comprises a signal transmitting and receiving device 10 and a signal transmitting and receiving device 20 that perform bidirectional communication via a transmission path 30. The signal transmitting and receiving device 20 comprises a driver 21, a filter 22, a receiver 23, and a controller 24. The receiver 23 recovers a clock signal by performing frequency locking on a training pattern signal output through the filter 22, and outputs a recovered clock to the controller 24. The controller 24 receives the recovered clock output from the receiver 23, controls a cutoff frequency of the filter 22, and controls an operation of the driver 21 based on a frequency information of the recovered clock signal.