A frame correlation determination part is for determining a level of correlation of decoded image signals between frames. A flat region detection part is for detecting an image region in which a difference in brightness between neighboring pixels is small as a flat region from the decoded image signals. A high-frequency region detection part is for detecting an image region including a high spatial frequency component as a high-frequency region from the decoded image signal. A smoothing processing part is for performing smoothing processing to the decoded image signal corresponding to a predetermined region. A processing region setting part is for setting an image region in which the smoothing processing part is to perform smoothing processing to the decoded image signal are included. The processing region setting part sets at least a region in frames in which a correlation between frames is low and which is a flat region and not a high frequency region in the decoded image signals, as a processing region.