An input image signal 101 is divided into MC block units and, when coding processing is performed in these divided units, a motion compensation section 107 generates a motion-compensated prediction image 106a by detecting movement amounts in predetermined MC block units, a smoothing filter section 124 performs, with respect to the prediction image 106a, smoothing of pixels located at the boundaries of adjoining MC blocks on the basis of predetermined evaluation criteria, and a prediction residual signal 108, which is obtained from the difference between the prediction image 106b obtained by the smoothing, and the input image (input image signal 101), is encoded. Accordingly, it is possible to use relatively straightforward computation to perform processing, with respect to a prediction frame image generated by block-unit motion-compensated interframe prediction (MC), to adaptively smooth a discontinuous waveform generated between MC blocks of the prediction frame image, whereby the efficiency of low bit rate coding that employs interframe MC is improved.