Method and apparatus for encoding/decoding image base on inter prediction

A method and an apparatus for encoding/decoding an image based on the inter prediction are provided to use the correlation between I(Intra) pictures and adjacent pictures simultaneously, thereby increasing the compression ratio of the image encoding. An extraction member(270) extracts intra prediction encoded blocks included to other pictures encoded previously. A prediction member predicts the present block from the extracted blocks. An encoding member(230) encodes the present blocks on the basis of the prediction. The pictures are the pictures included into the same GOP(Group Of Picture) as the present picture including the present block. The present blocks are predicted from the extracted blocks and I(Intra) picture included into the GOP. The extraction member extracts the number N blocks with the low compression rate among the Intra-prediction-encoded blocks included into the pictures.