An image data compression apparatus which compresses code data obtained by compressing image data by a fixed length encoding method so as to reduce a scale of hardware and reduce a development cost of software for an image data compression a binary image data processing part processes binary image data in accordance with a run length encoding method, the binary image data processing part including an encoding part which encodes run lengths of the binary image data by an encoding part. A multiple value image data processing part processes multiple value image data in accordance with a prediction encoding method. The encoding part of the binary image data processing part is commonly used by the multiple image data processing part so that the encoding part compresses both the binary image data and the multiple value image data.