In order to reduce the total capacity of a ROM used for adjustment of the black level and the white level of a digitized luminance signal for a television receiver, for example, a comparator compares the input luminance signal with a predetermined threshold value, a NOT gate inverts the input luminance signal, a first switching unit selects the input luminance signal or the output of the NOT gate, a ROM outputs an adjustment characteristic signal responsive to the output of the first switching unit, a multiplier multiplies the output of the ROM by a weighting signal and outputs the result of the multiplication as an adjustment value, a subtractor subtracts the adjustment value from the input luminance signal, an adder adds the adjustment value to the input luminance signal, and a second switching unit selects the output of the subtractor or the output of the adder.