An input image signal is divided into MC block units and, when coding processing is performed in these divided units, a motion compensation section generates a motion-compensated prediction image by detecting movement amounts in predetermined MC block units, a smoothing filter section performs, with respect to the prediction image, smoothing of pixels located at the boundaries of adjoining MC blocks on the basis of predetermined evaluation criteria, and a prediction residual signal, which is obtained from the difference between the prediction image obtained by the smoothing, and the input image signal, is encoded.