a table memory which stores combination of plurality of coded data each being a DCT coefficient represented in a Huffman coding method and corresponding bits to be embedded, and a plurality of new coded data each being a new DCT coefficient represented in Huffman coding method;

an input unit which inputs JPEG image data;

a block data acquisition unit which acquires block coded data of one block from the JPEG image data inputted by said input unit;

a first acquisition unit which acquires DCT coefficients represented in Huffman coding method, which are for embedding embed bits, from among comparatively low-frequency coefficients with the exception of DC coefficients in the block coded data acquired by said block data acquisition unit;

second acquisition unit which acquires, referring to said table memory, new DCT coefficients represented in Huffman coding method using the DCT coefficients acquired by said first acquisition unit and the embed bits; and

an updating unit which updates the block coded data by replacing the DCT coefficients acquired by said first acquisition unit with the new DCT coefficients acquired by said second acquisition unit,

wherein in a case where code length of the new DCT coefficients acquired by said second acquisition unit is different from that of the DCT coefficients acquired by said first acquisition unit, said updating unit adjusts code length of the JPEG image data and then updates the block coded data.