A singular point removing part (12) removes, from a degraded video signal and a reference video signal, singular points that are noise of invisible high frequency components. A pixel value correcting part (13) removes the bias of a pixel value added to the degraded video signal. The singular point removing part (12) converts the video signals to spatial frequencies to remove the high frequency components, and thereafter performs reverse conversions to restore the video signals. Alternatively, the singular point removing part (12) uses an averaging filter or median filter to remove the singular points. The pixel value correcting part (13) determines a correlation between corresponding pixel values of the reference and degraded video signals, and then corrects the pixel value of the reference or degraded video signal such that the pixel value of the degraded video signal is coincident with the pixel value of the reference video signal.