In an image processing apparatus, connected via an external bus to at least an external controller and an external storage device, input image data is processed by an image processor 2, then processed image data 1 and image data 2 are simultaneously stored into respective areas of an image buffer 4. The image data 1 is read from the image buffer 4 while it is stored in the image buffer, and the read image data 1 is processed by an image processor 5. The image data is outputted through an image output controller 6 and a bus I/F unit 1 to an external storage device 903 via an external bus 101. At this time, the result of processing on frame data by the image processor is preserved in correspondence with output of the image data 1 for one frame, and image processing and output processing on the image data 2 stored in the image buffer, for one frame, is started.