To provide a reversible coding method by which a compression rate is enhanced even for an image where correlation between adjacent pixels is small.

In this reversible coding method, image data are prediction- coded, prediction error data by prediction coding are divided into blocks, whether a block has a large prediction error or a small prediction error is discriminated for each block, vector quantization is applied to blocks with a large prediction error, a difference between a vector value of a code book retrieved by applying vector quantization to the blocks with a large prediction error and the prediction error is calculated, entropy coding is applied to the difference and the prediction error in blocks with a small prediction error, and coding data are generated by using the entropy code, a block quantity discrimination flag and an index by vector quantization.