PURPOSE: To shorten the time required for the start of transfer compressed data on an image data processor which divides the image by one page and processing it at a high speed.

CONSTITUTION: An image by one page is divided into plural parts and data of the divided images are processed by one compressor expander 6. The processed data are stored in FIFOs 8-1 and 8-2 provided corresponding to compressor expanders 6-1 and 6-2. The stored data are transferred by DMA to a compressed data storage means 11. A DMA transfer controller 9 which controls the transfer is previously actuated by a CPU 1 and starts transferring the data once receiving a DMA transfer requesting signal DRQ. The DMA transfer requesting signal is generated by DRQ control circuits 13-1 and 13-2 provided corresponding to the FIFOs. The DMA transfer controller 9 is already actuated, so once the DMA transfer requesting signal is inputted, the transfer is started in a short time.