A transmission characteristic compensation system enables to reduce the generation of transmission deterioration by estimating an initially selected control direction, and also to compensate in advance with a setting value estimation so as to suppress the generation of transmission deterioration in advance. The transmission characteristic compensation control system includes a variable compensator having a control circuit; and an optimal setting value calculation portion for calculating an optimal setting value for the control circuit, wherein the optimal setting value calculation portion estimates future transmission deterioration on a predetermined time-by-time basis to set into the control circuit the optimal setting value for compensating the estimated transmission deterioration performed by the variable compensator.