Bandwidth design is described for the amplifier and reshaping circuit that determine the receiving sensitivity of a digital optical repeater. Also described is the optimum adjustment of the operating conditions as determined by the combination of the amplification factor of an APD and the discrimination level. For the former, the required conditions are clarified for the clamp circuit as a low‐cut circuit. the relations are obtained between the peak value variation of the output voltage of the clamp circuit and the bandwidth of the reshaping circuit. For operating condition adjustment the repeater operation is formulated under various degradations and the relation between the causes of degradation and the SNR is analyzed. Based on these findings, various adjustment procedures are compared. It is shown that the system has sufficient tolerance to these degradations if adjustment is made for intersymbol interference.The present study provides a basis for choosing the conditions for the clamp circuit as a low‐cut circuit and the bandwidth for the reshaping circuit. A method of adjusting the operating condition is found that provides sufficient tolerance to degradation of an optical repeater.