PURPOSE: To automatically execute a correction processing, to eliminate necessity for the labor of a user and to always realize a picture with satisfactory picture quality by detecting the change of a waveform in the synchronizing signal of a video signal, discriminating the picture quality degradation condition of the picture caused by the video signal according to the degree of this change and controlling the picture quality.

CONSTITUTION: An input terminal 1, variable filter 2, noise reduction circuit 3, switch 4, output terminal 5, synchronizing separator circuit 6, subtraction circuit 7, peak detection circuit 8, noise detection circuit 9 and reference synchronizing signal generating circuit 10 are provided. From the synchronizing signal, the waveform change or a superimposed noise component is detected and from these detected results, the condition of the picture quality degradation is discriminated. Corresponding to the result of this discrimination, the correction processing or noise removal processing of the video signal is executed and the picture quality is automatically controlled. Thus, the labor of the user for executing operations is saved and the picture with the satisfactory picture quality is always obtained.