PURPOSE: To obtain a picture quality adjustment circuit which has a simple configulation and produces no error of timing for generating the asymmetrical secondary differential signals.

CONSTITUTION: A buffer circuit 11 receives the secondary differential signal of a luminance signal and then outputs it after the amplification or the input/ output impedance conversion. A clip circuit 12 clips the secondary differential signal and outputs it. A signal inverting circuit 13 inverts the secondary differential signal and outputs it. A synthetic resistance 14 adds together the output signal of the circuit 11 and the output signal of the circuit 12 in a ratio of 1:(1-K) where 0≤K≤1 is defined. Meanwhile, a synthetic resistance 15 adds together the output signal of the resistance 14 and the output signal of the circuit 13 in a ratio of 1:(1-L) where 0≤L≤1 is defined. Thus the asymmetrical secondary differential signals are obtained. An adder 16 adds the asymmetrical differential signals to the luminance signal.