Abstract: In an adaptive equalizing apparatus using quantized feedback, when the tap coefficients of a FIR filter are suddenly decreased due to a large noise input, or when the input signal level is suddenly lowered, the level of the input signal to the quantized feedback circuit becomes low, and the quantized feedback circuit malfunctions. Since the result of the quantized feedback circuit is utilized in the adaptive equalizing apparatus, the adaptive equalizing apparatus malfunctions, and cannot be restored to the normal operating state. To prevent the malfunction of the adaptive equalizing apparatus, as the first measure, limiters are inserted in the input lines of the tap coefficients of the FIR filter, the level of the signal entering the quantized feedback circuit is limited so as not to be lower than a specific value, thereby preventing the quantized feedback circuit from malfunctioning.