A substrate unit and other substrate unit are mounted with integrated circuits and are connected to a backboard via respective connectors. The substrate unit monitors a signal wave passed between the substrate unit and other substrate unit and detects a delay time and a gain of a reflected wave with respect to a signal wave, performs delay adjustment with respect to a cancellation wave based on the detected delay time, performs gain adjustment with respect to the cancellation wave based on the detected gain, and superimposes the processed cancellation wave on the signal wave thereby canceling the reflected wave.