To provide a method for making a receiving-sensitivity control parameter for deciding the receiving sensitivity of an optical receiving circuit automatically follow the optimum position by using the jitter value of a binary-equalizing-data signal obtained by binary-converting an input signal as a parameter showing the quality of the input signal. A binary-equalizing-data signal output from a limiter amplifier and a clock extracted by a clock-extracting circuit are input to a jitter-detecting circuit. The jitter-detecting circuit outputs a voltage corresponding to the jitter value of the binary-equalizing-data signal. A control circuit receives an output of the jitter-detecting circuit and performs an arithmetic processing by using a DSP or the like, and controls the identification voltage of the limiter amplifier so that the jitter value of the binary-equalizing-data signal (output of jitter-detecting circuit) is minimized.