An image compression apparatus performs quantization of DC component data, low-pass component data and high-pass component data which are generated by frequency conversion of still image data. An extracting part extracts additional data and coding object data which is to be entropy coded, from quantization data. An entropy coding part performs entropy coding of the coding object data stored in a coding object data memory. An additional data processing part generates a flex bit from the additional data. A pattern information generation part acquires the coding object data directly from the extracting part, to generate pattern information indicating whether the coding object data is zero or not. A bit stream generation part outputs the pattern information, the coding object data and the flex bit in a predetermined order, to output a bit stream.