A CPU executes decomposing processing based on data by a PDL received through a communication interface, and generates data by an intermediate language for each band. Here, the CPU judges whether or not the values of the image data are all zero as the image data in the band. As to the image data whose values become all zero, rendering processing from the intermediate language to the image data and compression processing of the image data by a JBIG compressor are omitted, and only a termination code is stored as coded data in a main memory. Thereby, the processing speed can be increased. A JBIG decompressor decompresses the coded data to generate output image data, which is outputted to a printing unit. Thus, the image processing device of the invention increases the speed of generating coded data, and enhances the total throughput.