PURPOSE: To suppress propagation of an error and to attain high compression by making a code quantity constant.

CONSTITUTION: An inter-frame prediction section 53 discriminates the similarity between inputted block data and a reference block to generate the reference clock thereby obtaining a prediction error. A compression mode selection section 50 gives data of an in-frame compression area to an orthogonal transformation section 16 as they are and data of an inter-frame compression area give a prediction error from the inter-frame prediction section 53 to the orthogonal transformation section 16. A quantization section 58 has an in-frame compression quantization table and an inter-frame compression quantization table, a quantization device selection section 54 selects a quantization means to quantize an orthogonal transformation coefficient. Since the inter-frame compression is adopted, high compression is attained.