To prevent ocurrence of the time delay, faults and errors of data by adding a pulse width detecting function to a reception squelch circuit to decide the normal or abnormal pulse width, controlling the threshold voltage in response to the input voltage control signal when the pulse width is normal, and eliminating the noises according to the detection result of the received data level and based on the controlled threshold voltage.

When the signals inputted to the non-inverting terminals of pulse detection comparators 70 and 80 have normal amplitudes, the control signals Cout1 and Cout2 of low states are outputted. Therefore, a 1st comparator 30 compares the input node voltage of a 2nd load resistance R2 applied to an inverted terminal with the output node voltage of a 1st load resistance R1 applied to a non-inverted terminal and outputs the positive threshold voltage VTHP after confirming that both signals Cout1 and Cout2 have low states and the pulse width of the received data is normal. In the same way, a 2nd comparator 32 outputs the negative threshold voltage VTHP. The noises which are generated when no received data are inputted can be eliminated.